Prime lens FL & FR for an APS-C camera to do AP?

[25585]

I am looking at prime focus lenses for my Fujinon mirrorless camera & am wondering what FL & FR would suit astrophotography, should I wish to dabble. I have a 27mm f2.8 and 50mm f2.8 at present. Max B shutter time is 60 min. 

[michael.h.f.wilkinson]

Both lenses should give nice wide views. I find that something like a 135 or 200mm also works very nicely indeed, on both full-frame and APS-C cameras.

[PeterCPC]

You could already take widefield images with the 27mm lens and stack them. You would need to restrict the exposures to about 10 secs on a tripod.

Peter

[25585]

No knowledge about stacking at all. Need a 101 course ?

[happy-kat]

Online budgetastro.net Doug has easy to get started guides, deep sky stacker and GIMP are free. You could get Dark Art or Magic Bullet from FLO of you are into reading paper.

[davew]

I can only speak for myself but if I had something like an X-T2 I'd be after a Samyang 12mm f2.

On a static tripod you could risk 25 seconds in the north and around 20 seconds facing south.

On a tracker I'd probably try the Samyang 135mm f2.

Dave.

[25585]

16 minutes ago, davew said:

I can only speak for myself but if I had something like an X-T2 I'd be after a Samyang 12mm f2.

On a static tripod you could risk 25 seconds in the north and around 20 seconds facing south.

On a tracker I'd probably try the Samyang 135mm f2.

Dave.

Looking for wide angle. How is the 12 wide open?

[davew]

I've read about this lens and seen quite a few images on the net. Ian Norman has a decent review and some real world images - https://www.lonelyspeck.com/rokinon-12mm-f2-0-ncs-cs-review/#more-2568

I've seen images from the 135mm not long after collection and directly off the laptop screen and have to say they were top notch. ( Sony E mount )

As many will warn you, Samyang QC isn't necessarily the best so test any lens you get. Even the big players have to be tested.

The Fuji alternatives are the 14mm f2.8 or the 16mm f1.4. 

Dave.

[Luna-tic]

2 hours ago, 25585 said:

I am looking at prime focus lenses for my Fujinon mirrorless camera & am wondering what FL & FR would suit astrophotography, should I wish to dabble. 

Same basic principles as land photography, with one major exception. 

The difference is that aperture no longer determines depth of field, which is unimportant in AP (it's all at infinity), but now becomes part of your exposure calculations along with Shutter speed and ISO. Focal length will determine your field of view and image scale, as usual. So, determine how large an area you want in an image, choose your focal length accordingly and get the largest aperture lens you can afford. A 300mm f/5.6 lens will allow shorter exposure times than a 300mm f/8, etc. with shutter speed and ISO the same.

Unlike land photography, you now have to contend with Earth's rotation, so longer exposure means the stars will move and you have to accurately track them, so shorter is better with exposure to keep the stars round. Stacking allows a series of short exposures to be processed to give the detail of a long exposure without the problems of movement. The longer the focal length, the more that movement becomes an issue.