ISCO ultra star red the actual stretch factor.

[Anton Zimin]

Hey everybody!

Finally I've bought an ISCO adapter as the one at the picture. It works great and focuses ok. But it seems it's not 2x at all. It 's a bit less. Does anybody know the actual stretch factor? To me it's about 1.88, but I'm not sure. 

The guy on this link says it is 1.9. To me seem it works ok.

[Julien416]

Focused at infinity? 

[Anton Zimin]

 

21 minutes ago, Julien416 said:

Focused at infinity? 

It's a bit not that sharp on infinity)) You can see it on a really far objects. I will try tomorrow again. 

 

 

Does any one have the optical scheme for this adaptor? 

[Julien416]

At close focus the stretch ratio WILL NOT be 2x... I told you the other day about breathing... It will most likely be 1.8x at close focus and 2x at infinity. 

[Anton Zimin]

Ok. Thanks! I will try tomorrow. Here comes the breathing! That's why you use diopter focus system. I have to check it. 

 

 

But anyone) where can I find the optical scheme of this lens? 

[Julien416]

It's probably a basic hypergonar formula. Just very well corrected and coated. Google it. 

If you have sharpness trouble, you might want to try a little bit before infinity on your taking lens. If it's not changing anything, try another taking lens. If it's not sharp, then your isco has alignment issues. Not that complicated to correct actually but still a little pain. 

[ken]

IMO, this lens is sharp enough and true 2x at infinity.  But it is the least flare lens.

[Anton Zimin]

I'm just wondering if there is a way to put it on a 35mm taken lens. 

20 minutes ago, ken said:

IMO, this lens is sharp enough and true 2x at infinity.  But it is the least flare lens.

there are always some filters available) 

[Zalem]

I had this lens for a while (and regret selling it).

I used to apply 1.75x stretch in post. Definitely not a 2x lens but it produces great images nonetheless.

Cheers.

[ken]

20 hours ago, Zalem said:

I had this lens for a while (and regret selling it).

I used to apply 1.75x stretch in post. Definitely not a 2x lens but it produces great images nonetheless.

Cheers.

I don't think so.  Definitely a 2x lens for me to use.  Here are 3:1 pictures from 3:2 sensor camera.

 

 

[Zalem]

7 hours ago, ken said:

I don't think so.  Definitely a 2x lens for me to use.  Here are 3:1 pictures from 3:2 sensor camera.

 

 

Cool, I guess there's no one answer to this question. As mentionned above, stretch factor could vary from close focus to infinity, or perhaps some copies simply have a different stretch factor.

Definitely a sharp lens, but fyi to my surprise my Kowa 16-D has produced sharper images than the Isco. Comes with its flaws however.

[ken]

13 hours ago, Zalem said:

Cool, I guess there's no one answer to this question. As mentionned above, stretch factor could vary from close focus to infinity, or perhaps some copies simply have a different stretch factor.

Definitely a sharp lens, but fyi to my surprise my Kowa 16-D has produced sharper images than the Isco. Comes with its flaws however.

IMO, they have the same sharpness for all these size lens.   The difference is the view angle.  ISCO can use 100mm without vignetting at infinity on FF camera.  16-D needs 135mm.