[Michael Piziak]

Just as I did with the Tamron mirror lens (comparing it to the Pentax 55-300), I sold that one. Now I'm comparing the Sigma 600mm F8 mirror vs. Pentax SMC 55-300mm ED to see if it's worth keeping.

Sigma 600 with auto-levels



Pentax 55-300



Sigma 600 cropped



Pentax 55-300 cropped



I found the Sigma images had a washed out haze-like/fog like affect that the auto-levels mostly cleared up, so I did an auto-levels on all the images.

I will add more images from both, both un-cropped and cropped, but my initial thoughs are that, like the Tamron, cropping the Pentax 55-300 images and Sigma 600 images to similar size on screen is resulting in better/sharper images from the Pentax 55-300. So, again, I'll post more images, but so far I'm finding photos out of the Pentax are resulting in better/sharper images and finding it to be a hard argument to hold on to images from the mirror lens... Everyone's comments/replies please...

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Last edited by Michael Piziak; 02-11-2023 at 12:59 PM.

[RICHARD L.]

If you're "patient", you will keep this Sigma Reflex maybe ... a week or a month. One month was the time I kept it, for real.

Never forget, "I told you so" ...

[Michael Piziak]

If you're "patient", you will keep this Sigma Reflex maybe ... a week or a month. One month was the time I kept it, for real.

Never forget, "I told you so" ...

Right...

I wander if I have a less than good copy or what, but there seems to be a lot of "washed out" images with this copy.

For example, below is an un-processed image from it. When I do an "auto-levels" it corrects most of it (it did a bit more contrast as normal I think):



And here is an image right out of the Pentax 55-300




For comparison, here's a post processed "auto-levels" done to the Sigma image:

[GUB]

The drop in contrast to some extent is exactly what I would expect from a mirror. Nothing the curves tool can't sort out. So light as highlights haven't been fried.
You seem to be operating in a very low light situation. Applying the good ol sunny 16 rule it would appear the environment is 6 to 7 stops darker than a sunny day with the mirror settings.
Interestingly the 55-300 is underexposed 2 stops in comparison - make that one stop to be explained after taking the slower tstop of the mirror and f7.1 of the zoom.
That difference in shutter speed can make a big difference in sharpness especially as the 1/125 is right in the middle of shutter shake zone if you have it set to mechanical shutter.
And for what is is worth the Mirror of the birdtable is significantly better than the cropped zoom one.
You are going to need Raw, utilising iso invariance as well as mastering critical focus , tripod use , electronic shutter etc to get the best out of the mirror. As I said elsewhere they are intolerant sods.
Crop of the two bird feeder shots taken from screenshots..

Attached Images

   

[robgski]

I am not surprised at these results, and thank you for showing them.
I have a 500mm mirror lens, and my experience is that the DOF is razor thin, so your focusing needs to be precise.
Even more importantly, with a fixed f8 aperture, the subject must be to be very will lit.
Mirror lenses seem to be prone to CA and PF, so using high ISO only makes the problems with the lens more noticeable.
FWIW, on a good day, a mirror lens can produce a good image, and TopazAI sharpening and noise reduction software helps.

[steephill]

Take care of the basics first. You are using a very long focal length which requires extra care to get decent results. Use a good stable tripod and perfect your manual focus technique using magnified Live View. Even on a solid tripod don't try slow shutter speeds which will only show subject movement. Shoot raw and adjust processing according to what you see. Avoid autolevels, it clips both highlights and shadows.

---------- Post added 12th Feb 2023 at 01:25 ----------

Mirror lenses seem to be prone to CA and PF

Mirror lenses are much less prone to CA than normal telephoto lenses.

[RICHARD L.]

Mirror lenses are much less prone to CA than normal telephoto lenses.

Exactly. The light travels twice through the Cassegrain design and chromatic aberrations cancel each other.

[Thagomizer]

My own rules for shooting with mirrors are:

a) only shoot in good light and

b) make sure your subject fills the field of view.

Violating either of these rules usually results in disappointment.

[Michael Piziak]

Under the right conditions, with little shake on a tripod and proper lighting, I can see a difference


600mm Sigma



Pentax 55-300




I think that on more brightly lit days, and a weighted down tripod, the mirror lens will show it's performance. Of course this was taken of a bird feeder hanging on a rope and the right side of the image is closer to the lens, perhaps showing the limited DOF of the mirror lens also. Also, this was an over cast day.

Addendum: I just realized how shaky the back porch is to be shooting with this lens, even with a tripod. Learning more about it....

[Michael Piziak]

Well, I never could get the Sigma mirror 600mm to take, the majority of, photos that were as good or better than cropped ones from my Pentax 55-300mm lens, so I ended up selling the lens.

It was fun trying to get it to work good - just wasn't for me. I was surprised at how fast it sold, though (for $99).....

Michael

[GUB]

Well you can't say we didn't tell you so

Old mirrors are just another brush for your art work - And some artwork is not about detail.