Can you compare a RASA 8 to a Canon 400mm f/2.8L photolens

[Alien 13]

4 hours ago, tooth_dr said:

You can but it’s tight with 44mm back spacing to the lens collar.  Taking 17.5mm back focus for the average camera leaves 26.5mm to fit filter wheel and adapters.  Atik EFW is 22mm so this just leaves 4.5mm for adapters.  Off the shelf Canon-M48 adapters measure 10mm.  This means you end up too far away and can’t reach focus at infinity.  I have made up a custom M54-Nikon lens adapter that has a length of about 7mm.  This works because the Nikon lens back focus is 46.5mm.  I think that you could use a EFW with this lens but it wound require a thin EFW (I think QHY make one at 17mm) and a custom adapter.

I think the 400mm Canon has a built in filter drawer for 52mm filters, not sure if the astro ones would fit but it could be a neat solution..

Alan

[tooth_dr]

26 minutes ago, Alien 13 said:

I think the 400mm Canon has a built in filter drawer for 52mm filters, not sure if the astro ones would fit but it could be a neat solution..

Alan

That is a neat solution, would be easy to 3d print a holder for them.  Unfortunately this leaves it pretty much the same as the RASA, where automated imaging with different filters isnt possible.

[Spongey]

5 hours ago, tooth_dr said:

You can but it’s tight with 44mm back spacing to the lens collar.  Taking 17.5mm back focus for the average camera leaves 26.5mm to fit filter wheel and adapters.  Atik EFW is 22mm so this just leaves 4.5mm for adapters.  Off the shelf Canon-M48 adapters measure 10mm.  This means you end up too far away and can’t reach focus at infinity.  I have made up a custom M54-Nikon lens adapter that has a length of about 7mm.  This works because the Nikon lens back focus is 46.5mm.  I think that you could use a EFW with this lens but it wound require a thin EFW (I think QHY make one at 17mm) and a custom adapter.

Using a QHY600 short bfl version or 268M with the corresponding filter wheel gets you to 34mm / 29.5mm respectively, which leaves you enough room for a 10mm lens adapter. I plan on using my 268M with my Samyang 135 in this way!

[festoon]

4 minutes ago, Spongey said:

Using a QHY600 short bfl version or 268M with the corresponding filter wheel gets you to 34mm / 29.5mm respectively, which leaves you enough room for a 10mm lens adapter. I plan on using my 268M with my Samyang 135 in this way!

Out of interest @Spongey which filter wheel did you pair with the 268M? There seems to be so many options in the QHY range!

[Spongey]

2 minutes ago, festoon said:

Out of interest @Spongey which filter wheel did you pair with the 268M? There seems to be so many options in the QHY range!

I am using the QHYCFW3M-US, which is 17mm thick. This is for 36mm filters

[tooth_dr]

13 minutes ago, Spongey said:

Using a QHY600 short bfl version or 268M with the corresponding filter wheel gets you to 34mm / 29.5mm respectively, which leaves you enough room for a 10mm lens adapter. I plan on using my 268M with my Samyang 135 in this way!

True.  It will only really work easily with the QHY wheel bolted directly into a thin QHY EFW. 

[nfotis]

There's an adaptor from Astromechanics for EF lenses, you can fit a filter wheel and a dedicated camera in the 44mm backfocus.

 

N.F.