Samyang 135mm F2- first impressions

[catburglar]

Had an opportunity to give my recently acquired Samyang 135mm F2 ED camera lens a run out last night on M42 and the flame.

It didn't quite go to plan, forgot to switch the camera to Bulb, so ended up acquiring 60x4s subs rather than the 60x30s I had planned. Got a few longer subs before Orion disappeared behind the trees......the image below is around 15mins of data using an unmodded EOS1300D......

First impressions:

F2 is fast- 30s subs at ISO 1600 put my histogram well over to the right, so will try ISO 800 next time

Focus is tricky at F2- used the Canon app on my smartphone but still not sure I nailed focus- might see if I can get a bahtinov mask

I need to get better at flats- I've tried using twighlight flats and my laptop monitor with sheets of paper as a diffuser, but still not good enough. I'm not even sure if DSS is applying the flats- it appears to do so, but the image stack with and without flats is not much different.

[Alien 13]

Lots of potential there I think, focusing at f/2 is never going to be easy but I would get rough focus first then zoom in X5 at which point you should start to see some faint Stars appearing then focus again on these, repeat the process again at X10 by which time the faint stuff should blink on/off with the tiniest adjustment.

Alan 

[Captain Scarlet]

I use the x10 on the back of the camera LCD, it seems to have been fine for me so far. Roger N Clark (clarkvision.com) advises going even further and using a hand-magnifier on the 10x. The biggest problem I've found is keeping careful not to touch the focus-band on the lens thereafter. Easy in principle but the number of times I've had to re-focus after forgetting...

Cheers, Magnus

[happy-kat]

I like dslr controller on my android devices for controlling and focusing the camera. If you turn the Iso up temporarily when you got focus the really faint stars show easier is a tip I use from Alien above.

[geordie85]

Focus rings and a bahtinov mask makes focusing easier.

Plus high ISO and x10 zoom as mentioned above 

[catburglar]

Thanks for the tips.....probably just need to be a bit more patient, but was probably a bit too keen to get some images which is why I forgot to change the exposure settings after focusing/framing

I’m really struggling with getting good flats. I realise the image above isn’t the best quality data, but whenever I try to stretch it the vignette becomes really  prominent.

I never had a problem with my canon zoom (but this was at f6ish, so perhaps unsurprising). Geordie85 - I’ve just seen your image in the Star Adventurer thread. Did you use flats or do you use gradient exterminator (or similar) to process the gradient out?

[kev]

May not be quite in focus but some of ghe structures there. Get the focus right and thats a winner

 

[geordie85]

5 hours ago, catburglar said:

Thanks for the tips.....probably just need to be a bit more patient, but was probably a bit too keen to get some images which is why I forgot to change the exposure settings after focusing/framing

I’m really struggling with getting good flats. I realise the image above isn’t the best quality data, but whenever I try to stretch it the vignette becomes really  prominent.

I never had a problem with my canon zoom (but this was at f6ish, so perhaps unsurprising). Geordie85 - I’ve just seen your image in the Star Adventurer thread. Did you use flats or do you use gradient exterminator (or similar) to process the gradient out?

I used flats, astroflat pro and gradient xterminator. Probably didn't need to use all 3 but better safe than sorry

[melsky]

I also have recently bought one of these lenses, here is a test shot I took this week with the lens mounted on my Atik One 6 through a 5nm HA filter. The lens was half a stop down at F 2.4 and this is a stack of 11 frames of 15 minutes each from a light polluted town in Oxfordshire. Images stacked in DSS and all processing done in Photoshop, I'm very pleased with the result.