[kayasaman]

The main focus of this session was pretty much to get some nightscape and astro shots done. The milkyway image has already been posted to the astro group: First ever nailing of the milkyway with detail - who said internal reflections?? - Astrophotography - PentaxForums.com

Unfortunately the place that was visiting is quite far away so it left me only 2 hours of play time.

I'll start with the Irix 150mm:












Moving over to my workhorse and best lens (though now with the limitations discovered it seems that I need to move on and opt for a different one), the Samyang 24mm f/1.4 is an excellent lens but I think has hit my frustration limit. The lens suffers badly from internal reflections which make is useless during bright sunny days, heavily moon lit nights, brilliant points of light, moist conditions, or dark scenes (ie. skies):















Unfortunately for everything it does well.... the limitations have really upset me right now:




For a lens which is supposed to be an astro master and specialist, what you're left with is:






This is my mw shot without using the star reduction script from Bill Blanchet in PixInsight (not the same file I posted in the astro group), you can see the image is completely hosed by the lens optical design:





Overall I am just really disappointed and frustrated right now. I need to find a solid wide angle lens that is ultra sharp. Yes there are options of course and I'm most likely leaning toward the DFA15-30mm at present as it gives several focal lengths in one which is advantages over having to purchase many different primes which is ok not a long list but still a list in itself.... Irix 15mm f/2.4, Irix 21mm f/1.4, Irix 30mm f/1.4, Irix 45mm f/1.4, Venus Lens Laowa 12mm f/2.8 are what come to mind right now.....


Uh.... what a nightmare :-( :-( :-(


Full album available here: https://photos.app.goo.gl/nfsNsFkL9D33RgVZ9

[Digitalis]

From user reports the superwide lenses from IRIX can suffer from sample variation compared to Samyang. You may have just had a bad bit of luck with this particular copy of the Samyang 24mm f/1.4 -from user reviews the lens has a solid reputation*. Using lenses wider than 20mm is ill advised for astro images due to the wider FOV incorporating more of the night sky, some stars will inevitably blur over time even with the K1 astrotracer active.


Don't overlook the Pentax DFA21mm f/2.4 Limited.

Pentax K-1 DFA21mm f/2.4 Limited


un-sharpneded 100% corner crop

* with an aggregate review score of 9.27 which puts it roughly in the same ballpark as the legendary FA31 which is no slouch optically.

[kayasaman]

Don't overlook the Pentax DFA21mm f/2.4 Limited.



Pentax K-1 DFA21mm f/2.4 Limited


un-sharpneded 100% corner crop

Ah this one: HD PENTAX-D FA 21mmF2.4ED Limited DC WR / Limited / Wide-Angle Lenses / K-mount Lenses / Products | RICOH IMAGING


I didn't see it.... all my eyes zoomed in on was APS-C for most of the wider primes.

[photoptimist]

Bummer....

However, I have a hard time imagining how a Milky Way scene could create a glowing ring like that. Are you absolutely sure that there were NO other lights (street lights, house lights, head lights, flash lights) anywhere in front of or off to the side of the lens? Any extraneous light reaching the inside of the filter ring or front element could certainly flare like that. Even if the light source isn't in the frame, it can ruin an astrophotograph.

Good luck!

[kayasaman]

Hiya, so if you look above there's a shot with a light in the middle and the moon to the left covered in mist. They were right behind me at the time. I was stood in front of that tree shielding the camera from both moon and that yellow light.

Now, having said that... one of the suggestions given to me in the astro group was related to histogram stretching. Basically the further you stretch, the more exaggerated things become.


This is a shot I did with the same lens but didn't push as far during stretching, I don't actually think I stretched the shot at all but you don't see the problem:




I'll just try stretching it now and report back my findings.

---------- Post added 05-03-23 at 05:50 PM ----------

Bummer....

However, I have a hard time imagining how a Milky Way scene could create a glowing ring like that. Are you absolutely sure that there were NO other lights (street lights, house lights, head lights, flash lights) anywhere in front of or off to the side of the lens? Any extraneous light reaching the inside of the filter ring or front element could certainly flare like that. Even if the light source isn't in the frame, it can ruin an astrophotograph.

Good luck!

I'm just reprocessing that image above from my comment, but it's unlikely that anything will come out of it. The reason is that it's only a 60s exposure. The milkyway shot was 11 shots @ 60s stacked which of course means you get 11 minutes of internal reflection.

This is another example which shows the magenta ring created by light sources at certain angles:




In terms of wide field astro this was done from my back yard in the middle of one of the heaviest light polluted cities around:





Actually with the image above I think there was too much cloud to show the issue....


You can't really see much from it:




However, if we look at other images... then you do actually see the white halo:




This area was Dark! no lighting whatsoever bar the moon to the rear - if I remember correctly?



---------- Post added 05-03-23 at 06:07 PM ----------

From user reports the superwide lenses from IRIX can suffer from sample variation compared to Samyang. You may have just had a bad bit of luck with this particular copy of the Samyang 24mm f/1.4 -from user reviews the lens has a solid reputation*. Using lenses wider than 20mm is ill advised for astro images due to the wider FOV incorporating more of the night sky, some stars will inevitably blur over time even with the K1 astrotracer active.


Don't overlook the Pentax DFA21mm f/2.4 Limited.

Pentax K-1 DFA21mm f/2.4 Limited


un-sharpneded 100% corner crop

* with an aggregate review score of 9.27 which puts it roughly in the same ballpark as the legendary FA31 which is no slouch optically.

By the way, I have heard this about the 12mm Irix but the 15mm and upwards should be solid. Strangely many people that I have been in contact with have told me that they had multiple copies of the Samyang 24mm then given up. It seems mainly the issue stems from decentering or optical alignment.

In terms of Ultra Wide lenses for astro.... AT kind of compounds the trailing by introducing rectilinear distortion effects meaning you get trailing primarily at the edges. I am actually wanting to work my way to a proper GOTO tracking mount then down the line dedicated monochrome cooled astro camera. The Moravian Instruments range has really taken my attention:
Products

Though in retrospect, I am told that the DFA15-30mm is actually sharper then the Irix 15mm.

One solution could be to go for the 15-30 then if I actually need f/1.4 go for a 21mm Irix.


Don't forget that these lenses will also be used for landscape too where you want wide :-)


I'll have to think about things though... ideally my thought was to get the f/2.8 zoom lineup as it's more versatile for traveling rather then lugging 50 different lenses around...

[AstroDave]

They were right behind me at the time. I was stood in front of that tree shielding the camera from both moon and that yellow light.

Do you have the viewfinder cover inserted during your exposure(s)!? Light may be coming in from the back of your camera.

[Digitalis]

One solution could be to go for the 15-30 then if I actually need f/1.4 go for a 21mm Irix.

The problem being with f/1.4 lenses is that aspheric elements of large diameter are quite expensive to manufacture, and even if they are incorporated into the optical design they may not completely correct for coma and astigmatism to the desired degree. In this respect I would temper my hopes and expectations. The DFA21 does quite well with astro, the only significant issue I can see is the rather severe vignetting @ f/2.4. From the crops I posted above, coma and astigmatism are well controlled. From user reports the vignetting on the Irix 21mm f/1.4 @ f/1.4 is worse....and this is assuming you luck out hard enough to procure a perfectly centered copy.

[kayasaman]

Do you have the viewfinder cover inserted during your exposure(s)!? Light may be coming in from the back of your camera.

Yes, the viewfinder over is on so not "backlight" so to speak

---------- Post added 05-04-23 at 05:42 AM ----------

The problem being with f/1.4 lenses is that aspheric elements of large diameter are quite expensive to manufacture, and even if they are incorporated into the optical design they may not completely correct for coma and astigmatism to the desired degree. In this respect I would temper my hopes and expectations. The DFA21 does quite well with astro, the only significant issue I can see is the rather severe vignetting @ f/2.4. From the crops I posted above, coma and astigmatism are well controlled. From user reports the vignetting on the Irix 21mm f/1.4 @ f/1.4 is worse....and this is assuming you luck out hard enough to procure a perfectly centered copy.

It's interesting that you say this. I mean other brands like Canon and Nikon have been doing f/1.4 lenses for eons and are especially popular with portrait guys from 50-80mm focal lengths.

The reason I'm thinking of f/1.4 is letting as much light in as possible. I normally run my Samyang at f/1.4 but recently I decided to use f/2.8 mainly for the diffraction spikes. Ok my location is still bright enough that I don't need to go beyond ISO 800. Like in one of the images I posted, I was all the way down at f/13 for DOF and then I needed to adjust the ISO but only to 1600 or so....

I mean f/1.4 is not mandatory... even f/1.8 will be fine. The old Nikon 50mm lens that came with our FM gen 1 SLR film camera for example is f/1.8... sure it's circa 1977 but still....

[Digitalis]

I mean other brands like Canon and Nikon have been doing f/1.4 lenses for eons and are especially popular with portrait guys from 50-80mm focal lengths.

Lenses in the circa 50~90mm FL range utilize designs that don't involve the same compromises that super wide angle lenses do, particularly when there is a mirror box involved.

f/1.4 lenses have a long history of compromises and slower lenses are generally easier to correct for various aberrations as their elements are of a more modest diameter. By that reasoning the Pentax 50mm f/1.2 would be a brilliant astro lens if only it wasn't for the fact that there is a horrendous amount of vignetting, coma and astigmatism at f/1.2 that make it a pretty abysmal lens at that aperture for astrophotography...stopped down it does fare better but there are slower and better corrected fast 50s out there.

[kayasaman]

Lenses in the circa 50~90mm FL range utilize designs that don't involve the same compromises that super wide angle lenses do, particularly when there is a mirror box involved.

f/1.4 lenses haev a long history of compromises and slower lenses are generally easier to correct for various aberrations as their elements are of a more modest diameter. By that reasoning the Pentax 50mm f/1.2 would be a brilliant astro lens if only it wasn't for the fact that there is a horrendous amount of vignetting, coma and astigmatism at f/1.2 that make it pretty abysmal lens at that aperture for astrophotography...stopped down it does fare better but there are slower and better corrected fast 50s out there.

Actually member eye.in.eye said the same thing about the 50 lenses over in the astro group. Though if you check out MossyRocks images using the Venus Lens Laowa 12mm, they are really impressive, even though he is using a K3. I know they are really good lenses but the problem is that they are not weather sealed which means that I can't use them in conditions where you have dust, rain or generally moisture in the air.

It's a difficult situation :-( Go wide and risk or go narrow and loose the width? Definitely for landscape I am not a fan of anything narrower then 30mm as it's too restrictive unless you're doing things specifically like trying to avoid trees or other elements getting into the scene.


By the way have you seen Ken Lee's astro images using the DFA15-30mm....? It might not be as fast as f/1.4 and probably wide open at f/2.8 doesn't have any diffraction spikes but it's definitely considered to be a fantastically sharp lens and good astro performer.

Weight doesn't bother me at all as I actually prefer having things a little more meaty in my hands, though of course it will always be on a tripod anyway.