Pentax 105/2.8 Super Takumar as a tube lens - big surprise!

[Beatsy]

Thanks for the pics. I think you're right - it is the extra 5mm of focal length that hides the vignetting, but the source of that vignetting is the objective itself. The 600D sensor is 22.3 x 14.9mm while the Sony A7rii crop mode uses a 24mm wide area, so it would probably show even more vignetting with that objective. It shows none with the Mitties on the same FL tube.

While I'm here - I just fiinished a deep test stack of my first critter with a 10x Mitty on the 105mm Takumar (5.25x on crop-mode sensor - covering 4.9mm FoV). Whole frame and a 100% crop below. I did no post processing at all (other than resizing the first and cropping the second for upload). SooC RAWs exported to TIFFs, stacked with PMax and uploaded as-is. No sharpening, levels or adjustments of any kind. No retouching either - so lots of transparent hairs and hazy bits. I even left the "streakies" at the bottom of the full frame (the foreground leg sagged a little during capture of the stack). Next one will be better...

I think you'll agree though, the base image quality is pretty darn good!

[mjkzz]

Yes, the objective almost touched the front lens for both SMC-100 and EF-100, I actually was afraid that they scratch those lenses.

OK, let me emphasize the qualifier that I am using MY OBJECTIVES, not mitties :-), so test result are for those objectives and it shows the difference, the extra 5mm COULD be the cause for the difference, nonetheless, it does help.

The reason I gave the SMC away the first place is because I have a 70-300mm zoom and played with it, with that zoom lens, I have to set zoom at 135 to reove vignetting, so I thought that is the limit for tube lens, and as matter of fact, I actually got a Zhongyi 135 as tube lens. But now, I know the lens is a factor, too. So, yeah, lens maters.

[Lou Jost]

It is very impressive that you were able to get down to 135mm with your 70-300 zoom without vignetting. The zooms I have tried cannot be pushed down very much without vignetting.

[mjkzz]

it is an old Nkikor 70-300, paid 99USD back in 2004

[Lou Jost]

May I ask which one? Do you like the results when used with an objective?

[mjkzz]

Ok, here we go. In stead of shooting a stack, I think shooting a flat surface should be sufficient, so the subject is a piece of white plastic foam. I think the extra 5mm focal length might be the reason, rather than the lens itself, nonetheless, the Pentax 105mm seems to have less vignetting.

Yes, single image is fine.

The most important difference between tube lenses is the location of the entrance pupil. Lenses that play well with objectives have an entrance pupil that is relatively far forward; lenses that don't, have it farther back.

The vignetting with your 4X objective may be due to the objective's limited field of view at its front end. My Nikon CFI BE 4X on EF 100mm f/2.8L IS USM has either significant corner darkening or none at all, depending on whether I remove the hood from the front end. (http://www.photomacrography.net/forum/v ... hp?t=18182)

--Rik

took out the hood for my 4x, I think it improved slightly, but not as much as to be decisive...but good to know another trick

[mjkzz]

I think you'll agree though, the base image quality is pretty darn good!

darn good? I think they are excellent.

[mjkzz]

Just want to show comparison between a Mitty 5X and a Mitty 2.5X QV. Since the QV 2.5X needs 100mm tube lens, so it should not have any vignetting so it is a good reference to compare to. [edit] If you squint, you can see slight vignetting for the Mitty 5x compared to the QV 2.5X[/edit]

[JH]

My experience is that sometimes a short empty tube between the lens and the camera can reduce vignetting.
Best regards
Jörgen Hellberg