DSLR lens for astrophotography

[Ponton]

Hi, so i am finally getting into astrophotography. I know there is a steep learning curve. I already purchased a Canon 600d, intervalometer and ordered an ioptron skyguider pro + tripod.  I will only use DSLR + camera lens for now and maybe in the future upgrade.

I do want a Samyang/Rokinon 135mm but it's not easy to find one right now. Currently there is two used lenses i can buy close to me that i find interesting: Samyang/Rokinon 85mm f1.4 or the Sigma 150mm f/2.8 Apo macro DG HSM. I can get the sigma for about 300£ and the Samyang for 190£.
I read some good things about the Samyang 85mm but haven't found much about the Sigma 150mm when it comes to astrophotography. Seems that you can't set the aperture manually on the Sigma due to it being a macro lens and it stops down when changing focus if i understand it correctly?

 

I mainly want to capture images of nebulae.
I know the differences in focal length between these lenses is big.

So my question: is any of these lenses good or should i consider anything else?

[Icesheet]

If it’s primarily for astrophotography and your willing to push a little further then you might consider the Askar FMA 180. Have a search on here for some good info on it. 

[PeterCPC]

Amazon have got the Samyang 135mm on their site.

On E Bay too.

Edited April 9, 2021 by PeterCPC

[Chefgage]

As with all astro gear/photography gear it's a waiting game at this time. If you are willing to wait for delivery I would recommend getting the Samyang 135mm. Compared to my other lenses (canon) the build of this lens if a lot better. I was most impressed by the focus ring which is fairly stiff. This in my limited experience makes focusing easier. Also the size of the body of the lens.makes fitting dew heaters easier as they don't get in the way of the focus ring like they do on my other lenses.

[Stuf1978]

I have a Sigma 150mm F2.8 Macro lens and I've used it for astro a few times and it gives acceptable results, one thing to note is that it's very sensitive to focus and can be susceptible to coma if the focus isn't bang on. I'm not sure where you read that you can't change the aperture manually but you can, it's just like any other lens  I took this using it:

 

[Ponton]

On 09/04/2021 at 14:55, Stuf1978 said:

I have a Sigma 150mm F2.8 Macro lens and I've used it for astro a few times and it gives acceptable results, one thing to note is that it's very sensitive to focus and can be susceptible to coma if the focus isn't bang on. I'm not sure where you read that you can't change the aperture manually but you can, it's just like any other lens  I took this using it:

 

Wow that is really nice. I just lost my chance buying the sigma so I think i will go for the Samyang 135mm, as Peter said it is available on Amazon right now.  Thanks for all your answers and help.

 

I have another question. I just aimed my camera at the night sky last night from my balcony with my kit lens for fun and i seem to get a lot of walking noise across the image with just 2 sec exposure and iso 800. Here is the photo where i have only adjusted the levels a bit. To the left there is a straight line and to the right of it it the image gets lighter. When i try to process it more it gets very distinct. What is the line and how can i counter the walking noise? Is it usual even at these short exposure times?

[Stuf1978]

20 hours ago, Ponton said:

Wow that is really nice. I just lost my chance buying the sigma so I think i will go for the Samyang 135mm, as Peter said it is available on Amazon right now.  Thanks for all your answers and help.

 

I have another question. I just aimed my camera at the night sky last night from my balcony with my kit lens for fun and i seem to get a lot of walking noise across the image with just 2 sec exposure and iso 800. Here is the photo where i have only adjusted the levels a bit. To the left there is a straight line and to the right of it it the image gets lighter. When i try to process it more it gets very distinct. What is the line and how can i counter the walking noise? Is it usual even at these short exposure times?

Is that a single image or a stack? The line to the left looks like what you get when the framing of several exposures is not quite the same after stacking.

As for the other issue, I can't see any walking noise. If you are referring to the horizontal lines across the entire image is looks like banding that is pretty common with canon dslrs. 

[irtuk]

If you are stacking you need to start building up a library of calibration images, which are flats, darks, flat darks and bias frames I think .. I am not entirely sure of the precise difference between a flat dark and a bias frame yet, I am quite early in my astrophotography adventure myself!

[EntropyTango]

Most lenses are pretty good these days

And if you buy new at least you have a warranty just in case it doesn't perform

I use an old Pentax 135mm F2.5 with good results

[EntropyTango]

5 minutes ago, irtuk said:

If you are stacking you need to start building up a library of calibration images, which are flats, darks, flat darks and bias frames I think .. I am not entirely sure of the precise difference between a flat dark and a bias frame yet, I am quite early in my astrophotography adventure myself!

With most DSLR's and lenses I found dark frames and bias frames to be most important. Flat frames less so

So when starting out just go for light, dark and bias. Most DSLR lenses cover their frames quite well

Generally you settle for ISO speed which is a compromise between noise, colour and gathering those precious photons

I find I use ISO 1600 mainly

 

[irtuk]

if you have Photoshop you can use this attached PSD image I have been playing with this afternoon to try and improve my workflow.

I have made one group of layers called "Processing" that has the stretching and levelling in, then another group of layers that are images from DSS with varying sets of calibration frames applied to the same base set of lights ( except the last one.. ) 

 

You can then turn off each base image layer to reveal the layer below it, which has increasingly more calibration frames, and the last one has also jumped from 17 to 111 light frames. I was quite surprised to see the quality difference jumping from 10 to 70 Dark frames, its removed a lot of noise increasing those. I am currently shooting some more.

Demo Image of Impact of Darks - Flats - Bias - Offset.psd