Lenses for astro/nightscape photography.

Steiwa

Using Samyang 14mm F2,8 for astro, but my plan was to look at the new Irix 15mm F2,4. Looks exiting.

http://irixlens.com/15mm

Ironheart

spraynpray said:

Well, my night sky lens of the moment is the 24-35 Sigma. Aberrations are good, focusing is easier than the Samyang 24/f1.4 plus you have a super sharp zoom with AF for landscape.

One thing a little off piste: Is it me or is the D750 a complete swine to try to focus in black conditions? The random colour noise that plagues the live-view screen is absolutely wretched. Is it mine or do others have the same problem with it? My mates 6D and 7D2 are far easier to focus.

Have you tried enabling exposure preview in the "i" menu? Page 61-62 in the manual. Otherwise the display tries to always give you a visible picture, by ramping brightness up or down automatically. On the D500 you just press "ok" when in live view, on the D750 I think you have to menu surf a bit.

I was also wondering why you use a 10x loupe when the live view screen can zoom 15-20x? This is how I achieve critical focus for any tripod shot...

spraynpray

@Ironheart: Yes, I have exposure preview enabled (it is under the i button when in live view). I am fully zoomed in and using the loupe but have tried all zoom settings with and without the loupe. The screen is fizzing with noise whereas my mates Canons are clearer so he nails focus every time without a loupe and so can I when I try his gear. This is really pi$$ing me off as I have lost a lot of shots by not having achieved critical focus.

spraynpray

@framer: You are severely limiting your results by going for lenses which have apertures that start that small. Best star count is large max aperture used 1 click smaller to tame aberrations a little. 24mm f1.4 has clear aperture of 17 whereas the 15/3.5 is only 4! There is obviously an impact on shutter speed the longer the focal length and also an impact on aberrations the wider you go. put into example an 85/1.4 is 60 but shutter speed is short (2.4S) if not tracking. The 20/1.8 is 11 but shutter speed is 10S. As most people want foregrounds sharpish so aren't tracking, wider a

It's all about compromise f.o.v. VS shutter open time.

Ironheart

@spraynpray how about turning exposure preview off then? Better or worse?

spraynpray

I was thinking the same while I was typing so I'll do that tonight and let you know tomorrow. If it is that simple I will feel pretty stoopid! Isn't the first time and won't be the last though... ;-)

Ironheart

Also, making sure your aperture is wide open will help. From page 56:

A Previewing Focus During Live View Photography (P, S, A, and M Modes Only)
To temporarily select maximum aperture for an improved focus preview during live view photography, press the Pv button. To return aperture to its original value, press the button again or focus using autofocus. If the shutter-release button is pressed all the way down to take a picture during focus preview, aperture will return to the original value before the photo is taken.

spraynpray

Yeah, it's wide open at f2 all the time at night really.

spraynpray

OK, I have found a fiddle to get round the problem. I Compose the image using exposure preview and find a bright star near the middle of shot to zoom in on (100%), then turn off exposure preview and critically focus.

I am also prone to accidentally touching the focus ring in the pitch black too so I am looking for a really wide rubber band to put over the rear joint between the focus ring and barrel to add friction to the manual focus action. The lens hood doesn't do much to keep condensation away, so I will leave it reversed to act as a partial guard for the rest of the focus ring.

I wish I could find a fast wide high quality lens with a hard stop at true infinity and very low aberrations.