10 replies to this topic

[hxnduke]

Hi all,

 

I just bought a Samyang 135mm f/2 and I'm looking to use it with my ASI533MC camera. I will be replacing its bayonet with the M48 adapter sold by Astro Essentials. From my research online, this lens requires a 44mm backfocus. My camera comes with the necessary adapters for 55mm backfocus (top picture of this). My thought is that by replacing the 21-mm T2 extender in that schematic with a 10-mm T2 extender, I should be able to achieve the 44-mm backfocus.

Does this sound like a good plan or am I missing anything here?

 

Thank you for your inputs!

 

 

[JOEinCO]

This would be an excellent question for the Imaging Forums.  

 

[t-ara-fan]

That spacing will work. But a few things to think about:

• I think that camera can benefit from having a UV/IR cut filter. With your plan there is no room to put in a filter.  You could keep the bayonet on the lens, and use the ZWO EOS adapter. A filter can fit inside the ZWO adapter.  That gives you the option of using a DualNarrowband filter too.
• If you just want T2 adapters, the Baader VariLock 29, lockable T-2 ExtensionTube 20-29mm with spanner tool will let you adjust backspacing. 

 

I have been working on setting up my fast lens (105mm f/1.4) and it is incredibly fussy about backspacing.  And tilt.  I would say get the ZWO adapter and a set of fractional millimeter T2 spacer rings.

Edited by t-ara-fan, 26 January 2023 - 02:31 PM.

[hxnduke]

This would be an excellent question for the Imaging Forums.  

 

Beginners.jpg

Oh goodness, I totally meant to post this in Beginner Deepsky Imaging. My apologies!

If any moderator sees this, please feel free to lock/remove it. I will repost it on the other forum.

 

 

That spacing will work. But a few things to think about:

• I think that camera can benefit from having a UV/IR cut filter. With your plan there is no room to put in a filter.  You could keep the bayonet on the lens, and use the ZWO EOS adapter. A filter can fit inside the ZWO adapter.  That gives you the option of using a DualNarrowband filter too.
• If you just want T2 adapters, the Baader VariLock 29, lockable T-2 ExtensionTube 20-29mm with spanner tool will let you adjust backspacing. 

 

I have been working on setting up my fast lens (105mm f/1.4) and it is incredibly fussy about backspacing.  And tilt.  I would say get the ZWO adapter and a set of fractional millimeter T2 spacer rings.

Thanks for your inputs. I actually do use a dual-band filter (l-extreme) but since I thread it directly onto the front of the camera sensor, that doesn't add anything the optical path length. If I decide to go with an automated filter swapping solution, it will likely with a filter wheel. For this scenario, the schematic #2 on the link I showed should likely work since the OFW and its T2 adapter adds 22mm, making the total backfocus 45mm (6.5+22+16.5). We'll see how it works in practice though. 

[Ionthesky]

In case nobody notified a mod yet, I sent a tickler.  Duke, you'll likely get more hits when this moves over.

 

Regards,

Dave

[DeepSky Di]

Topic moved in accordance with forum rules. Enjoy!

[idclimber]

Instead of getting a 10mm spacer, I would get a set of adaptors that would allow you to fine tune this dimension. A set of 0.1mm to 1mm shims and a set of T2 spacers are very handy when dong this kind of thing. Agena probably has the best selection of these kind of parts. 

 

Otherwise your logic seems good. 

[DeepSky Di]

Here’s an old topic of mine where I tried to get a filter drawer into the gap: https://www.cloudyni...-lens-no-focus/

[HubSky]

Did you get the Canon mount version of the Samyang?  I was thinking that because of the 44mm back focus. 

 

Is so, ZWO makes a filter drawer adapter for Canon mounts that along with the 17.5mm for the 533 will give you 44mm. 

 

https://astronomy-im...er-for-eos-lens

[hxnduke]

Instead of getting a 10mm spacer, I would get a set of adaptors that would allow you to fine tune this dimension. A set of 0.1mm to 1mm shims and a set of T2 spacers are very handy when dong this kind of thing. Agena probably has the best selection of these kind of parts. 

 

Otherwise your logic seems good. 

Thank you. I hadn't thought of using thin shims for fine-tuning. I'll look into that.

 

 

Did you get the Canon mount version of the Samyang?  I was thinking that because of the 44mm back focus. 

 

Is so, ZWO makes a filter drawer adapter for Canon mounts that along with the 17.5mm for the 533 will give you 44mm. 

 

https://astronomy-im...er-for-eos-lens

Yes, it's the Canon version. I was looking at the ZWO adapter; however, I saw some comments saying that the bayonet coupling would tend to introduce tilt so ended up going with the Astro Essential version instead. Another reason is that I'm getting a manual M48 rotator so need some additional room. 

[hxnduke]

I had first light with this lens last night. Since my adapters for the ZWO camera have not arrived, I decided to try it out with my modified T1i camera and a CLS-CCD filter. I used it at f2.8 and ISO 800. There was vignetting around the corners but flats and some background extraction in Siril seemed to do a good job removing it.

I'm attaching the final stacked (43x120s lights, 18 flats, and 20 dark flats) and post-processed (Siril) image together with an unedited fit frame below. Any suggestion would be highly appreciated since I haven't worked with such widefield previously. Some specific questions:

• Does the focus look fine? I used a Bahtinov mask and focused against Capella.
• Does there seem to be any tilt issue here?
• For post-processing, any suggestions on how to handle objects with different magnitudes such as M42 and the Horse head here? As you can see, M42 is quite overexposed in the final stretched image.
• Any other suggestions or issues that you can see?

 

https://drive.google...FmG?usp=sharing

 

Thank you for your input!

Edited by hxnduke, 27 January 2023 - 12:56 PM.