49 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.

[Figo2018]

Thanks for the feedback guys

[dcaponeii]

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.

Completely wrong.  Stop giving such bad advice to novices or I'll be forced to report you to a moderator.

[Jan_Fremerey]

Completely wrong.  Stop giving such bad advice to novices or I'll be forced to report you to a moderator.

I don't think newbies and moderators will need your help in judging images taken with 2.4 µm at f/5 or equivalent.

[CrazyPanda]

I don't think newbies and moderators will need your help in judging images taken with 2.4 µm at f/5 or equivalent.

Anything that was taken at F/5 using a 2.4 micron camera would have looked better and more detailed at F/12 assuming seeing supports it.

 

Also, the images on that site are disingenuous because the capture resolution is lower than the final image resolution. There was clearly upsizing going on, probably through some form of drizzle or other enlargement, but life isn't CSI. You can't just "enhance" and create detail from nothing.
 

This is an example of what I'm talking about.

 

 

Had that image been *captured* at the resolution it was enlarged to, and sufficient data had been collected, it would look smoother, more crisp, and more detailed. It's clear from that image that it has been enlarged beyond the details that were really present in the image, and that noise dominates the finest visible details.

Edited by CrazyPanda, 25 July 2023 - 10:28 AM.

[Jan_Fremerey]

Had that image been *captured* at the resolution it was enlarged to, and sufficient data had been collected, it would look smoother, more crisp, and more detailed.

I don't think so. Please note that the factor 2 was just applied to prevent the display grid from becoming visible, see here. Surely you have better results on hand - "smoother, more crisp, and more detailed" - that you'd like to share?

Edited by Jan_Fremerey, 26 July 2023 - 07:20 AM.

[Mitchell Duke]

I don't think so. Please note that the factor 2 was just applied to prevent the display grid from becoming visible, see here.

Reducers do not help planetary imaging at all. This is very bad advice. In planetary you are using high magnifications, and small roi's. Why would you want to work against that. Introducing more glass and aberations will not help. Its best for the op to just image at the native or use extension tubes to just barely raise up to the 5x criteria.

[Jan_Fremerey]

Introducing more glass and aberations will not help.

So why use a Barlow when camera resolution with 2.4 µm at f/10 is already better than optical resolution? My f/5 setup with 2.4 µm camera is completely without glass.

[CrazyPanda]

So why use a Barlow when camera resolution with 2.4 µm at f/10 is already better than optical resolution? My f/5 setup with 2.4 µm camera is completely without glass.

He means when you have a properly sampled imaging train.

Makes no sense to use a focal reducer, and then a barlow.

Just use a barlow to get a more optimal resolution.

There’s zero reason to use a focal reducer. Unless you had really small pixels (like 1.2 micron pixels)

Edited by CrazyPanda, 26 July 2023 - 10:06 AM.

[Mitchell Duke]

So why use a Barlow when camera resolution with 2.4 µm at f/10 is already better than optical resolution? My f/5 setup with 2.4 µm camera is completely without glass.

First off read the post again, I said extensionnnnnnn!   If the op wants to get to 5x the camera's pixels you need to extend it slightly. 

An extension would help get to 5x or even 6x. 

[Jan_Fremerey]

If the op wants to get to 5x ...

Why get to 5x when 2x already fits optical resolution even under good seeing conditions, see here? 2x will allow 6x shorter shutter times and 6x more images to stack in a given time.

[Jan_Fremerey]

There’s zero reason to use a focal reducer.

With a quality 0.63x reducer you may have twice as much illumination on your camera chip for reduced shutter times, more frames per second, and flat field correction over a wider field of view.

[Mitchell Duke]

With a quality 0.63x reducer you may have twice as much illumination on your camera chip for reduced shutter times, more frames per second, and flat field correction over a wider field of view.

For DSO imaging yes that is correct. However we are only using a small portion of the chip. All of the above items are useless. You should really give it a try before knocking it down. Just trying to help!

[Jan_Fremerey]

For DSO imaging yes that is correct.

People may use their planetary setup for extended DSO imaging at high resolution as well, such as e.g. M3, or for planets including their moons, and not to forget shutter times and frame rates.

Edited by Jan_Fremerey, 26 July 2023 - 11:10 AM.

[CrazyPanda]

With a quality 0.63x reducer you may have twice as much illumination on your camera chip for reduced shutter times, more frames per second, and flat field correction over a wider field of view.

If you want more frames per second, you don't want to be using the whole sensor.

 

The ZWO ASI 224MC is one of the fastest cameras on the market, giving a clean 140-150FPS at full resolution, but that's still not as fast as you should be imaging. If you want more than that, you need to crop the sensor down. When I shoot with my 8" LX90 (non ACF), I shoot at F/20 at 5ms exposures and ~350 gain. 5ms is plenty short enough to freeze motion blur from the atmosphere, and if it's not it means the planet is too distorted to get clean images anyway, and it doesn't matter how short the exposure time is.

 

The only way to get 5ms exposure (200FPS), is to set an ROI. A wide corrected field is irrelevant for high resolution planetary imaging, and if you want to shoot the Moons, you should either be shooting them individually and then compositing them into a final image using a screenshot from Sky Safari or reference from WinJupos, or just taking a widefield reference shot to help with positioning.

Edited by CrazyPanda, 26 July 2023 - 11:16 AM.

[Mitchell Duke]

People may use their planetary setup for extended DSO imaging at high resolution as well, such as e.g. M3, or for planets including their moons, and not to forget shutter times and frame rates.

Yep did all of that this winter. They are very different procedures and processes than planetary.

[Jan_Fremerey]

If you want more frames per second, you don't want to be using the whole sensor.

I always want maximum possible illumination on my camera chip under consideration of image resolution.

[Mitchell Duke]

I always want maximum possible illumination on my camera chip under consideration of image resolution.

Ok? Im going to leave this one alone 😂😂😂😂

[Jan_Fremerey]

Ok? Im going to leave this one alone

You may stay happy with your 5x rule while I don't worry about newbies.

[BGazing]

I don't think so. Please note that the factor 2 was just applied to prevent the display grid from becoming visible, see here. Surely you have better results on hand - "smoother, more crisp, and more detailed" - that you'd like to share?

There's a ton of great photos in the planetary section of this forum where people use 5x and 7x regularly. 

[Jan_Fremerey]

There's a ton of great photos in the planetary section of this forum where people use 5x and 7x regularly. 

Nothing against 5x and 7x !! - I just try to demonstrate with practical examples that 2x works quite well and should be advantageous in view of shutter times, frame rates, field of view, and saving barlows.

 

Would you kindly show us 5x - 7x results for comparison with cited 2x results?

Edited by Jan_Fremerey, 28 July 2023 - 03:37 PM.