JimH123 Loc: Morgan Hill, CA

I was testing an old Minolta lens affectionately named "The Mini Beercan". It is a 35-70 zoom with a constant f4. I wanted to see how well it did for distortion as I find that only some lenses are good enough for images of stars. Many have objectionable coma distortion, and also equally disturbing astigmatism. As you will see, even when shooting f4 on a full frame camera, there is no real noticeable distortion. Other than only being f4, which means it doesn't suck in as many photons, it is a really good lens for stars.

Image #1 is one of the 6 originals that I am going to stack. It is 35mm at f4 and ISO 1600 for 15 sec. I didn't want star trails, so I limited it to 15 sec. And at 15 sec, there are also, limited numbers of stars that it sees.

Image #2 is the result of stacking 6 images in DSS. The background is rather grey and you can see it is in need of some cropping.

Image #3 is after a trip to Photoshop where the image has been stretched to darken the sky and enhance the stars. Many more can now be seen.

I actually have 11 Minolta lenses. Only a handful of them pass the distortion test:

1. 35-70mm f4 "The Mini Beercan"
2. 70-210mm f4 "The Beercan"
3. 100mm f2.8 macro
4. 50mm f2.8 macro

Some of the Minolta lenses that don't make it:

1. 20mm f2.8 -- Too much coma and astigmatism on brighter stars.
2. 50mm f1.7 -- Too much coma and astigmatism on brighter stars.

Image #1, one of 6 originals

(Download)

Image #2, Output of DSS

(Download)

Image #3, After a trip to Photshop

(Download)

Oknoder Loc: Western North Dakota

Just a quick question are testing only at wide open or are you also testing at different apetures? I only ask because I have a couple lenses, Nikkor 180mm as an example, that shows issues at 2.8 but when stopped down 1-2 stops performs astoundingly.

JimH123 Loc: Morgan Hill, CA

My ojective was to shoot with each lens wide open and to see the amount of distortion. And I was able to identify some of my lenses as sharp enough to do this without noticeable distortion.

In addition to the 4 Minolta lenses I previously have mentioned, I have several more lenses that are sharp enough to shoot wide open without showing distortion.

1. Tamron 24-70mm f2.8 - the entire range is sharp
2. Tamron 70-200mm f2.8 - the entire range is sharp
3. Rokinon 14mm
4. Tokina 300mm f2.8

I have some other lenses that are sharp enough if stopped down a couple stops, but these ones that I have identified can do it wide open which is how I want it for stars.

I wish I could say this about my fast 50mm lenses. I have several, and none are sharp enough wide open. This changes if stopped down a couple stops, but then that defeats the purpose of using a fast lens.

Minolta 50mm f1.7
Vivitar 50mm f1.8 -- m42 mount
Pentax 50mm f1.8 -- m42 mount

Minolta Rokkor 50mm f1.4 -- MC mount, can only use it on my A6000

I also find that the noise level is a bit lower on my A99 and A77ii than on my Sony A6000.

Oknoder Loc: Western North Dakota

Good to know about the Rokinon, as I was looking for one of those.

I have found that for the most part, macros work great because they are designed to a higher standard along with a fairly flat field. I love my Nikkor 200mm only wish it was f/2.8 not f/4. Maybe if they ever decide to remake/update that lens I'll be first in line.

Matthew

JimH123 Loc: Morgan Hill, CA

Yes, I have been astounded by the image quality of the macro lenses. The focus motor is geared down so that the lens hits focus with the absolute best accuracy and the lens produces such a nice flat field. These lenses are not as popular for general purpose because they focus slower. But I find that on landscapes, that the results are stunning.

SonnyE Loc: Communist California, USA

Hey Jim, Any idea what the two streaks are at 3 O'clock on image #1? I was looking for irregularities and found them.
At first I thought a satellite. But two? In the same frame? Parallel? :shock:

They are gone in the DSS image #2.
And long gone in image #3 post photoshop.

Sadly, the only beer cans I have are in the recycling barrel.
But I do have my Tamron 180mm... :)

Oknoder Loc: Western North Dakota

I'll bet your 180 will out perform my 200 micro simply because yours is 2.8 I believe and should produce lovely flat wide fields. You could find out the correct backspacing and make yourself an adapter to utilize your CCD even.

Matthew

JimH123 Loc: Morgan Hill, CA

Good catch Sonny. I can only guess what these are. Something is moving through the image and the upper track has a discontinuity in it and stops, and then a moment later, resumes slightly higher. Only a UFO can make sudden moves like that???

I have zoomed in (a lot) and posted the image and the streaks can be seen.

Images 2, 3, 4, 5, 6 do not have these streaks, and of course, DSS will have filtered this out as something that didn't belong.

So maybe I should call the UFO Reporting Center?

Actually, I have had parallel satellite tracks in other images, so it is not entirely unheard of. Most are much brighter than these, so I have to suspect that whatever it is coming from is very tiny. It doesn't have the look of planes which have blinking lights which periodically light up. And instead, it is a continuous brightness which is more in line with satellites. Sometimes a satellite will have a candy cane type striping indicating that it is rotating and one side is darker. But these are so dim. The shutter was open for 15 sec, it was a medium wide angle at 35mm and the streaks cover some considerable distance, so they are moving quite rapidly. And they certainly are dim! Probably in excess of 12th magnitude in brightness would be my guess.

The Streaks

(Download)

JimH123 Loc: Morgan Hill, CA

Now that is some comparison I would like to see. Do it once using the camera and again using the CCD and to then compare results. And again, this is going to vary a lot from one CCD to another.

SonnyE Loc: Communist California, USA

Glad I brought it to your attention. You know, that might be a keeper.
Yes I saw that disconnect in the upper track. I too, thought it rather odd, and it didn't appear in the lower track. :shock:

During an alignment Monday night I watched a satellite (?) moving from an Eastward to Westward direction in my telescope with my eyepiece.
I don't remember which star I was aligning on at the time, Mirfak would be my guess, or maybe Hamel.

:lol: 6 months ago I could barely find Polaris. Now I'm finding UFO's traveling parallel in your photographs. :roll:

I did a screen shot and if this works...

Bigger, Better...

(Download)

SonnyE Loc: Communist California, USA

Huh.
Never did one of those before, but it worked.
Sorry about the trash of screen 2.
But the jag shows. ;)

OH! And it's zoomable!

Great catch Jim! I would recommend you keep that Photograph.

JimH123 Loc: Morgan Hill, CA

For screen shots, google the word "cropper" and find https://cropper.codeplex.com/

This is a great utility to copy any portion of the screen. You can set it up to send the results to the clipboard and then to repaste them into something else. Although I find my email "Windows Live Mail" doesn't want to accept the paste. But if I paste it into the Windows App "Paint.exe" and then select it and do another CTRL C, that it now pastes into my email. Go figure!

At work, I use Outlook 365, and it accepts the pastes just fine.

Albuqshutterbug Loc: Albuquerque NM

My money is on Geo Synchronous satellites.
I get them when I shoot long exposures on the Orion Nebula all the time and occasionally up to 4 of them at a time.
They don't move but your tracking tripod does causing the streaks as you go past them.
;)

http://www.uglyhedgehog.com/t-349410-1.html
There's one in this shot that I posted.

http://www.uglyhedgehog.com/t-233981-1.html
This has a two fer. ;)

JimH123 Loc: Morgan Hill, CA

In this case, it would not be a Geo Synchronous satellite. The image was wide angle (35mm) and only 15 sec. Whatever caused these streaks was moving fairly rapidly as would be seen in something in low earth orbit.

Oknoder Loc: Western North Dakota

I have a few images with similar artifacts, I debayaered my images and fount they only existed in the green channel. I took it to be an artifact from the camera processing after Image integration. Mine changed directions but only in 90degree arcs. The bad thing with DSLRs is they are not truly linear in their integration.