RASA 8 Questions

[symmetal]

After seeing all the great images produced by this scope with short exposures, more suited for cloudy UK, I've decided to splash out on one, along with an ASI2600MC. 😊 The 2600 may be some time in being in stock so I could try it with my ASI071MC in the meantime as they have the same 17.5mm 'backfocus' distance.

I'm wondering how people use it with 2" filters like the IDAS NBZ. The 25mm scope backfocus is with the clear glass kept in the rear of the RASA8. Would it not be better to remove the clear glass as it's only there to allow the Celestron light pollution filter to be used instead, without affecting the back focus. It seems 2" filters like the NBZ can be fitted there instead if the 2" mounting ring is removed but that seems a bit fiddley.

If there is no filter or clear glass present I would expect the back focus to be more like 24.3mm so a spacer of around 6.8mm is needed with 17.5mm 'backfocus' cameras rather than the usual quoted 7.5mm spacer. 🤔

Artesky make a filter holder which with the ASI2600 gives the stated 25mm backfocus, presumably with the RASA8 clear glass filter removed. If not using the NBZ filter a 2" UV-IR cut could be inserted here instead rather than putting the RASA 8 clear glass back in to maintain 25mm backfocus.

What do people here do when imaging RGB concerning backfocus, and do they leave the clear glass in the RASA-8? Is there any alternative to using the Artesky filter holder? The Starizona holders sold by FLO don't work with 17.5mm 'backfocus' cameras. 365Astronomy sell the Artesky or perhaps buy it direct from Italy, or from TS.

Thanks for your help. 🙂

Alan

 

 

[iapa]

I just bought (2nd hand) a Starizona Filter slider for ZWO cameras which is sized to allow the existing clear glass filter to remain in place.

I plan to uses this with an ASI294MC cooled pro and a dual band filter

[tomato]

Initially I removed the Celestron clear window and put my un-mounted NBZ dual band filter in this location,but as you say, it was a bit fiddly. I also wasn’t keen on the soft backing material attached to the supplied Celestron adapter, preferring a solid machined face contact to reduce variation on assembly.

Fortunately I have access to machine tools so a hybrid QHY 268c/RASA8 adapter was made which can accommodate a screw in 2” filter. It is essentially the same set up as the Artesky unit. I have included the dimensions, but the adapter was made specifically for attaching the QHY version of the IMX571c camera.

[symmetal]

Thanks @iapa, but the Starizona Filter holder is for cameras with 6.5mm back focus like your ASI294. The ASI2600 and ASI071 have 17.5mm back focus so the filter adapter can be no more than 7.5mm thick to maintain the RASA-8 backfocus distance. 🙂

Thanks @tomato for the details of the adapter you made. It must be handy, having access to machine tools. 😀 Looks like I'll be getting the Artesky adapter though there's no hurry as I'll be trying it wideband for a while I imagine.

What do you do when wideband imaging? Do you put the RASA glass back in and use your adapter with no filter or use a 'clear' filter in your adapter? To save having no extra glass in the way was my reasoning for having say a 6.8mm spacer between the 2600 and RASA, rather than the standard 7.5mm spacer with the clear RASA glass in place.

Alan

[iapa]

12 minutes ago, symmetal said:

Thanks @iapa, but the Starizona Filter holder is for cameras with 6.5mm back focus like your ASI294. The ASI2600 and ASI071 have 17.5mm back focus so the filter adapter can be no more than 7.5mm thick to maintain the RASA-8 backfocus distance. 🙂

 

 

Sorry, I misread tho compatible cameras list, thought listed 1600 and 2600 - need new glasses.

[tomato]

1 hour ago, symmetal said:

Thanks @iapa, but the Starizona Filter holder is for cameras with 6.5mm back focus like your ASI294. The ASI2600 and ASI071 have 17.5mm back focus so the filter adapter can be no more than 7.5mm thick to maintain the RASA-8 backfocus distance. 🙂

Thanks @tomato for the details of the adapter you made. It must be handy, having access to machine tools. 😀 Looks like I'll be getting the Artesky adapter though there's no hurry as I'll be trying it wideband for a while I imagine.

What do you do when wideband imaging? Do you put the RASA glass back in and use your adapter with no filter or use a 'clear' filter in your adapter? To save having no extra glass in the way was my reasoning for having say a 6.8mm spacer between the 2600 and RASA, rather than the standard 7.5mm spacer with the clear RASA glass in place.

Alan

Hi Alan,

For wideband imaging I swap out the NBZ for a 2" IR/UV cut filter, so the Celestron clear window is now resigned to the spares box.

[symmetal]

30 minutes ago, tomato said:

Hi Alan,

For wideband imaging I swap out the NBZ for a 2" IR/UV cut filter, so the Celestron clear window is now resigned to the spares box.

Thanks tomato. That's what I thought would be most convenient. I'll do the same. 🙂

Alan