Canon converter used with Leica photo adapter on Televid 77

[Grimaldi]

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Hello everyone.

I own a Leica APO Televid spotting scope. I recently purchased a photo adapter 800mm f10.4 plus T2 mount ring. I have a Canon 5D markii DSLR that couples to the adapter. I have some excellent results. I was wondering if anyone might be able to answer a question please. If I bought an extender, let's say a 2X version, would this double the f stop to f20.8? The f10.4 on the adapter optic is fixed at that aperture. 

Thanks for taking the time to read my question

Grimaldi

  

[jankap]

That is correct. The extender takes away 50% of the incoming light, so 2 stops are gone. It takes it away after the lens so-to-say. But modern sensors allow to recover dark pictures. I have here a Celestron refractor and use the R tele-extender with it. A combination, that is not transportable.🤭

[Grimaldi]

hello jankap

Thank you very much for your reply and explanation. I might take a chance on buying one now. 

[jankap]

On 2/28/2022 at 1:51 PM, jankap said:

That is correct. The extender takes away 50% of the incoming light, so 2 stops are gone. It takes it away after the lens so-to-say. But modern sensors allow to recover dark pictures. I have here a Celestron refractor and use the R tele-extender with it. A combination, that is not transportable.🤭

 Wrong jankap, sit down, bad mark for you!

A 2x extender steals 75% of the light. Correct is, that one has to expose 2 f/stops longer (f/22 instead of f/11), that means one has to to take an exposure time 4 times longer (for example instead of 1/100s then 1/25s).

 

[jankap]

On 2/28/2022 at 2:49 PM, Grimaldi said:

hello jankap

Thank you very much for your reply and explanation. I might take a chance on buying one now. 

It depends on, what you want to do, but there are 1.4X extenders too.

[jaapv]

Normally 1.4 extenders provide better optical quality, but that might be of less interest for a spotting scope.