Lens Mathematics help needed

[GraphyFotoz]

Ok I have one for you DSLR Guru's/Pro's!

1st off I cannot afford $600+ for a fast Bird lens!

So I have scored a Tokina 2x Teleplus Converter for my efforts.
I would couple this with my Canon 75-300 USM f4-5.6.

Now I know that 2x300x1.6 =960mm (In 35mm terms)

Now where my hangup is....will this even be feasible F stop wise?
Not sure what the damage will be with the 1.6 crop factor?:scratch

Not sure of the mathematics for the F stop would be with this setup?:dunno


*** I do realize I will need to shoot on a bright day with a tripod with all this ***

[ian408]

I see 2 full stops for the 2x MC7 DG.

[GraphyFotoz]

I see 2 full stops for the 2x MC7 DG.

So we are talking around f8?

[pathfinder]

Ok I have one for you DSLR Guru's/Pro's!

1st off I cannot afford $600+ for a fast Bird lens!

So I have scored a Tokina 2x Teleplus Converter for my efforts.
I would couple this with my Canon 75-300 USM f4-5.6.

Now I know that 2x300x1.6 =960mm (In 35mm terms)

Now where my hangup is....will this even be feasible F stop wise?
Not sure what the damage will be with the 1.6 crop factor?:scratch

Not sure of the mathematics for the F stop would be with this setup?:dunno


*** I do realize I will need to shoot on a bright day with a tripod with all this ***
The f5.6 of your 75-300 zoom will drop to f11. It will not allow autofocus any longer, and manual focus at f11 will prove less than satisfactory. 2X TCs cost two stops of light - you really need to start with an f2.8 lens to use 2X TCs very easily, and at least an f4. Zooms will suffer optically also when used with a 2x.

[wxwax]

So, f11. I wonder what the bokeh looks like at 960mm f11?

[Bob Bell]

Ok I have one for you DSLR Guru's/Pro's!

1st off I cannot afford $600+ for a fast Bird lens!

So I have scored a Tokina 2x Teleplus Converter for my efforts.
I would couple this with my Canon 75-300 USM f4-5.6.

Now I know that 2x300x1.6 =960mm (In 35mm terms)

Now where my hangup is....will this even be feasible F stop wise?
Not sure what the damage will be with the 1.6 crop factor?:scratch

Not sure of the mathematics for the F stop would be with this setup?:dunno


*** I do realize I will need to shoot on a bright day with a tripod with all this ***

Well you don't mutiliple the crop factor because its just reducing your field of view not increasing your focal length which in the case of birds is very useful.

There are a lot of times when you need 5.6 to 11 because of light. My goal is to keep the SS above 1000 and that means ISO 400 and F8. That is going to be tough with a 2x when you start at 5.6.

Does the TC pass to the body that it is a TC? If it doesnt it would give you 600mm at 5.6 and your bodies meter will fix the exposure and you could get away with that. You will need a lot of ISO 400 or maybe 800. If your TC does pass the info, tape the 3 pins by themselves and see what it does.

Lastly, the TC is going to amplify any shake you have. When I put a 1.4x on my 400 it shows it in the viewfinder so good long lens technique is very important.

[GraphyFotoz]

Man it don't look good!:(:
I guess I'll hafta try it and see what happens.:dunno
Yeah I knew I'd hafta go manual focus...that was a given.

Well I only paid $50 for the 2x so I figured I'd give it a shot.

There is always my Sigma 105 Macro f2.8 and farther away Butterfly shots!:D

[JimM]

Well I only paid $50 for the 2x so I figured I'd give it a shot.

If it doesn't work for you and you want to sell the TC for $50, please put me first on the list to buy it.

[gus]

Graphy...just an observation. You always say that you cant afford the good stuff but you are always buying something of lower quality & never really appear happy with your results. If i was you i would scrap buying 5x somethings that might do the job & just bite the bullet for one good lens that WILL do the job. Remember they will outlast most anything else in the digital world.

Stuff is only expensive if you have to buy it twice.

[ian408]

Graphy...just an observation. You always say that you cant afford the good stuff but you are always buying something of lower quality & never really appear happy with your results. If i was you i would scrap buying 5x somethings that might do the job & just bite the bullet for one good lens that WILL do the job. Remember they will outlast most anything else in the digital world.

Stuff is only expensive if you have to buy it twice.

How very true.

[DoctorIt]

Might be beating a dead horse here, but I thought I'd mention that the TC might not even physically fit on your 75-300mm. As I recall, the element protrudes pretty far back on that consumer grade/compact zoom.

And for the record, I agree with Ian. In fact, I kinda learned that lesson for myself. When I switched to Nikon it was my goal to "do it right" even if it meant having less stuff. So now I may not have everything covered, but I now have a pro-level body (yes, it's a generation.5 outdated) and the best 70-200mm lens money can buy for my primary focus - bicycle racing.

As my photo mentor always said: forget all the crap, fast glASS baby!

[GraphyFotoz]

Might be beating a dead horse here, but I thought I'd mention that the TC might not even physically fit on your 75-300mm. As I recall, the element protrudes pretty far back on that consumer grade/compact zoom.

And for the record, I agree with Ian. In fact, I kinda learned that lesson for myself. When I switched to Nikon it was my goal to "do it right" even if it meant having less stuff. So now I may not have everything covered, but I now have a pro-level body (yes, it's a generation.5 outdated) and the best 70-200mm lens money can buy for my primary focus - bicycle racing.

As my photo mentor always said: forget all the crap, fast glASS baby!

It's not crap when ya can't afford $600 or more for a fast lens.
Ya make due.

[GraphyFotoz]

Graphy...just an observation. You always say that you cant afford the good stuff but you are always buying something of lower quality & never really appear happy with your results. If i was you i would scrap buying 5x somethings that might do the job & just bite the bullet for one good lens that WILL do the job. Remember they will outlast most anything else in the digital world.

Stuff is only expensive if you have to buy it twice.

:agree your right I just have this problem with tinkering with stuff I guess.:rolleyes
The good thing is I don't buy anything I cannot get my $$ back on.

But at least I have SOMETHING in the mean time.

[mercphoto]

Lens math made simple. :) Apertures are based on square roots of two, which is approximately 1.4. This is why you see lenses with f-stops of 1.4, 2.8 (which is twice 1.4), etc. If you start at 1.0 and multiply by 1.4 you get the following f-stops:

1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, etc.

Notice the pattern: every second number doubles. Its not a hard pattern to remember once you see the pattern. So, two stops from 5.6 is 11.

Now, why square root of two? Because the amount of light an aperture lets in is proportional to the area of the aperture, but the f-stop number for an aperture is related to the radius of the aperture, not its area. The area is proportional to the square of the radius. To double the area of a circle you don't double the radius, you increase the radius by the square root of 2.

[wxwax]

I think it's good advice. But only you know how much you can budget for this crazy expensive hobby.

[ivar]

Lens math made simple. :) Apertures are based on square roots of two, which is approximately 1.4. This is why you see lenses with f-stops of 1.4, 2.8 (which is twice 1.4), etc. If you start at 1.0 and multiply by 1.4 you get the following f-stops:

1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, etc.Hey, that's cool to know, i always wondered. (i'm a beginner, can you tell? :D) Maybe there should be a "learn a thing a day"-thread or something

[GraphyFotoz]

Hey, that's cool to know, i always wondered. (i'm a beginner, can you tell? :D) Maybe there should be a "learn a thing a day"-thread or something

Dude your in a hobby that's a non stop learning experiance!:D :thumb
Pro or not!!

[GraphyFotoz]

Lens math made simple. :) Apertures are based on square roots of two, which is approximately 1.4. This is why you see lenses with f-stops of 1.4, 2.8 (which is twice 1.4), etc. If you start at 1.0 and multiply by 1.4 you get the following f-stops:

1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, etc.

Notice the pattern: every second number doubles. Its not a hard pattern to remember once you see the pattern. So, two stops from 5.6 is 11.

Now, why square root of two? Because the amount of light an aperture lets in is proportional to the area of the aperture, but the f-stop number for an aperture is related to the radius of the aperture, not its area. The area is proportional to the square of the radius. To double the area of a circle you don't double the radius, you increase the radius by the square root of 2.

Doesn't f6.3 fit in there some place? I have seen that on some lenses also. :scratch

[mercphoto]

Doesn't f6.3 fit in there some place? I have seen that on some lenses also. :scratch
Yes there is an f/6.3. Its not, however, a full integer stop from any of the other standard stops. Its about a half-stop from 5.6 (or 8 for that matter). My list simply stated what numbers are full stops away from other stops.

[GraphyFotoz]

Yes there is an f/6.3. Its not, however, a full integer stop from any of the other standard stops. Its about a half-stop from 5.6 (or 8 for that matter). My list simply stated what numbers are full stops away from other stops.

Kewl thanx for your info...I'm sure it not only educates me but also others!:thumb

[Bob Bell]

Yes there is an f/6.3. Its not, however, a full integer stop from any of the other standard stops. Its about a half-stop from 5.6 (or 8 for that matter). My list simply stated what numbers are full stops away from other stops.

I always thought that was 6.3 then 7.1 which would make it 1/3 stops. Half stop would be around 6.7. I wish I could remember the math on some of these stuff I forgot 15+ years ago.

[DoctorIt]

It's not crap when ya can't afford $600 or more for a fast lens.
Ya make due.Yeah well, whatever. I shouldn't have put that comment in, because you probably ignored the better advice: check your lens for whether it will physically be able to fit a TC - TC's have glass too, and on shorter lens, the glass will bump, making it impossible to even mount the lens on the TC!

This turned into a nice discussion on f-stops, but it did start as a TC question.

[ian408]

Lens math made simple.

Nice post Bill!

ian

[GraphyFotoz]

Yeah well, whatever. I shouldn't have put that comment in, because you probably ignored the better advice: check your lens for whether it will physically be able to fit a TC - TC's have glass too, and on shorter lens, the glass will bump, making it impossible to even mount the lens on the TC!

This turned into a nice discussion on f-stops, but it did start as a TC question.

No offense taken! :thumb
I'm making note of all this!!!

My future dream is to grab me a Sigma 170-500mm DG.
Not the fastest lens but no way I can generate enough $$$ for anything L in a long focal length.
Gonna be a bit before I rack up the paypal $$$.
Trust me I have plenty of stuff to put on ebay to raise a few extra bux.
Selling stuff I don't use or want on ebay keeps me going in this hobby.
Sold off almost all my Model car hobby to fund what I have and did quite well too! Most stuff I got 2x to 3x what I paid for it.
I have sold everything on ebay from a 10K Charm Bracelet that was gonna go in the trash cleaning out an estate (Bought my Dell Computer with that $400)
to selling a 1984 Ford Thunderbird for a friend(made $200 commission)
I hit garage sales and fleamarkets now and then too.
Can't believe how fast high ticket stuff sells on some of these forsale forums!!!(Esp FM!)
PPL have $1000 or more just kick'in around? Must be nice!!:rolleyes
Me and my Wife don't make a wad like some do to toss at camera goods.
Our pay hasta go to bills and our family.**Not making any digs at anyone just an observation**
I know I tend to buy a fair amount of low ticket stuff but it keeps me going threw the Winter looking forward to getting goodies in the mail and such.
I don't spend any more on something than I can get back out of it in case I out grow it or it don't work for me.
(My boy has a AF EOS *film* camera so what don't work for mine might work on his as well)
Kinda like at kids Christmas revisited. :lol4

Sorry for the long winded reply just clarifying some things.

[Red Bull]

What does your gear consist of?

I went with Gus' advice. I would rather wait a while longer to save up the money for good stuff. Not only do you get better stuff, but you appreciate it much more since you worked so hard to get it. I didn't go cheap and get the 70-300 consumer-grade lens. I saived up and went for the 70-200 f/4L. IMO, it was worth it.

Just save up! I'm sure it wouldn't be as hard as I have it. I'm 16 and have no job. I have to rely on birthday and Christmas money and small jobs that my dad gives me.:rofl

[GraphyFotoz]

What does your gear consist of?

I went with Gus' advice. I would rather wait a while longer to save up the money for good stuff. Not only do you get better stuff, but you appreciate it much more since you worked so hard to get it. I didn't go cheap and get the 70-300 consumer-grade lens. I saived up and went for the 70-200 f/4L. IMO, it was worth it.

Just save up! I'm sure it wouldn't be as hard as I have it. I'm 16 and have no job. I have to rely on birthday and Christmas money and small jobs that my dad gives me.:rofl

Yup your right but I'm thinking of one better.....a Sigma 70-200mm f2.8.
Then if I add my 2x tele it won't slaughter my F stops to nothing!:thumb

[DoctorIt]

Yup your right but I'm thinking of one better.....a Sigma 70-200mm f2.8.
Then if I add my 2x tele it won't slaughter my F stops to nothing!:thumbI was just gonna suggest the Sig 70-200/2.8 or the 100-300/4. I've had both, and they superior to the 170-500. That lens is a dinosaur. you'd be way better off either of the first 2 and a TC. I had the 100-300/4 with a 1.4x Sigma TC - gave me a 420/5.6 at the long end and I had it all new in the box for under $1k.
:nod

[gtc]

bucks are an issue with me too,plus the $Aud exchange rate bites even further so i suggest you google for the Novoflex 400mm follow focus lens with gunstock and chest brace ,its an oldy but goody-manual but fast trigger operated focus(bellows at rear of lens) and they are designed for centre sharpness which is what you want for birding-there are lots of them around in the US and Europe and they go for not too much money-they are fairly light too,so you can swing them around quickly.