4 replies to this topic

[Figo2018]

I own a celestron 9.25 sct with a zwo ansi 183 what Barlow lens would be good for my scope(I am a beginner)

[Tulloch]

Best results (demonstrated over many years of imaging by numerous experts) are obtained when your focal ratio is around 5x the pixel size of the camera, in the case of 183 this is around f/12.

 

It might be best to start without a barlow with this setup, there should be some advantage in getting a 1.5x barlow in the future when your skills improve (note that the C9.25 has a native focal ratio of a little under f/9 without the diagonal). 

 

More tips and hints can be found in the FAQ.

https://www.cloudyni...d-january-2023/

 

Andrew

Edited by Tulloch, 20 March 2023 - 04:58 PM.

[Jan_Fremerey]

I own a celestron 9.25 sct with a zwo ansi 183 what Barlow lens would be good for my scope(I am a beginner)

With your f/10 scope the 2.4 µm pitch of an ASI183 would rather allow using a quality 0.63x reducer for better illumination and wider field of view including flat field correction. 2.4 µm, in fact, is suitable down to f/5 for high resolution imaging of even moon and planetary detail under good seeing conditions, see here. On deep sky in view of seeing related blur you may additionally employ 2x2 binning in order to reduce data transfer rates.

[Tulloch]

With your f/10 scope the 2.4 µm pitch of an ASI183 would rather allow using a quality 0.63x reducer for better illumination and wider field of view including flat field correction. 2.4 µm, in fact, is suitable down to f/5 for high resolution imaging of even moon and planetary detail under good seeing conditions, see here. On deep sky in view of seeing related blur you may additionally employ 2x2 binning in order to reduce data transfer rates.

Wrong

[james7ca]

I agree with Andrew, you probably don't need a barlow with your 9.25 SCT. Since this is the planetary imaging forum it's good to point out that with the 2.4um pixels on the ASI183 you're already approaching critical sampling with that camera even without using a barlow. But, you might eventually want to use a weak barlow for you planetary work particularly if your ASI183 is the color version. If worse comes to worse you can always try to drizzle your planetary images to get slightly more image scale which might lessen even further any need for a barlow with your SCT.

 

Also, as you get more into planetary imaging you'll probably want to use an Atmospheric Dispersion Corrector (ADC) and those tend to work a little better at slower f-ratios (although even f/10 isn't that bad, but f/15 might even be better).

 

As for barlow brands or types, IMO it doesn't make much difference for planetary work. However, if you plan on also doing lunar imaging then you might want to try something a bit more expensive than a bargain brand, perhaps even something that is telecentric. Unfortunately, most barlows won't offer a really wide and flat field as you might like for lunar imaging and some will also cause disturbing reflections when imaging the moon (particularly with an SCT). But, it's hard to know what barlows are going to work well with any particular SCT until you actually try to use it.