Ha filter size?

[TheMan]

I currently own a 72ed f/5.5 refractor with a orion field flattener for short refractors and I am thinking of buying a ZWO ASI178MC-C Cooled Colour camera. I would also like to buy a Ha filter that is 12nm (can't afford 7nm). I pretty sure the Ha filter size has to be 50mm to fit but I am not 100% sure. Any advice is appreciated.

[john2y]

Keep in mind that if you'll get colour camera, that it has bayer mask and if you'll use it with Ha filter, only 25% of the light will get to the sensor and you have to subtract another 19% from those 25% due to the quantum efficiency losses. Also I wouldn't really recommend ASI178 for deepsky, it has tiny sensor with tiny pixels. In that regard I think that ASI294 is much better way to go, I know it's more expensive but it has much bigger sensor, pixels and resolution. If you look at the comparison of the two, the 294MC Pro is the winner https://compare.astronomy-imaging-camera.com/

About the filter size, you don't need 2'' filter, your optics aren't that fast to get any vignetting with 1.25'' filter. Just get 1.25'' adapter to the telescope and use the smaller filter and the money you save up on the filter use for the better ASI camera ;-)

[vlaiv]

ASI178mcc is versatile camera, but indeed check if you will be satisfied with it.

It can be used for both DSO and planetary imaging due to being CMOS and having small pixels. For your scope it will be good because your focal length is short. If you use non reducing flattener - you will get 1.25"/pixel. That is good resolution for DSO work, but will demand good tracking / guiding. If your field flattener has reduction factor - that would be even better.

If you have longer FL scope - you can use it as planetary camera as well. Having OSC means that you will be able to shoot color images without additional filters (it even has IR/UV cut built in).

Filter size that you will need is basic 1.25". ASI178mcc sensor is small and there will be no vignetting. Also adaptation for 1.25" is straight forward - you can put it in special adapter close to sensor. I believe that such adapter is included with camera. If not, this is adapter that you will need:

https://www.teleskop-express.de/shop/product_info.php/info/p9003_ZWO-T2-Filter-Holder-for-1-25--filters.html

It let's you attach filter and still have T2 thread left to attach camera to scope, like this:

 

You can work with color camera and Ha narrow band filter, and it will almost be as john2y said - you will get 25% of the light - but not quite that low. Due to bayer matrix properties on most OSC cameras - in fact each pixel will record some signal - QE is never exactly 0 for all pixels. To get the most out of OSC and Ha filter, you really need to do special processing and it's complicated. However you don't have to go for best possible result straight away (until you learn and understand special processing).

Simple red channel stacking will get you Ha image straight away, but will as mentioned have 25% efficiency.

Next level would be to use full sensor (not just red channel) and use flats (flats will correct for different quantum efficiency). This will improve resolution, but can actually get you worse data in terms of SNR than previous method.

Best method that you can use to stack Ha with OSC is to use flats, split subs into 4 parts (each bayer pixel into its own sub) and use stacking method that can deal with different level of SNR. This will half your imaging resolution, but will give you best image in terms of SNR.

 

[Adam J]

5 hours ago, TheMan said:

I currently own a 72ed f/5.5 refractor with a orion field flattener for short refractors and I am thinking of buying a ZWO ASI178MC-C Cooled Colour camera. I would also like to buy a Ha filter that is 12nm (can't afford 7nm). I pretty sure the Ha filter size has to be 50mm to fit but I am not 100% sure. Any advice is appreciated.

If you want to do that then you would be so so much better off picking the ZWO ASI178mm-c (mono sensor) its even cheaper than the color camera on FLO right now so there can be no excuse at all not to get it.  

You will only need a 1.25 inch filter for the Ha, I recommend Baader as they have better anti-reflection coatings than ZWO and the difference in band pass is not that significant. The Baader 7nm is cheaper than the 12nm Astronomic as far as I recall. 

Grab a beginner set of LRGB filters (~£60) and a ZWO manual wheel (easiest way to fit 1.25inch filter to your setup) and you will be away and imaging with much much better results in comparison to the color version. 

The 178m is small but will have a ok field of view at 400mm. Better if you slap a 0.8x reducer on your scope. It will fit a sufficient number of objects in the FOV to keep someone new to the hobby interested for quite some time. You can fit in M42 for example, but you miss out on the running man next to it. Sometimes its nicer to focus on sections of larger targets in more detail too.   

Pixel for pixel the 178m is actually better than the larger 183m due to its 14bit A/D and it is 100% suited to DSO imaging, so long as you are ok with the FOV as per the above para.  

If i was on a more restricted budget the ASI178mm-c would be my choice of sensor. The image below shows how the camera will frame M42 at 400mm focal length. You have to imagine that the image extends up to the white line (which represents the sensor FOV) as opposed to just being the image in the center. For me that is good enough for a budget camera. 

Adam

 

[Adam J]

4 hours ago, john2y said:

Keep in mind that if you'll get colour camera, that it has bayer mask and if you'll use it with Ha filter, only 25% of the light will get to the sensor and you have to subtract another 19% from those 25% due to the quantum efficiency losses. Also I wouldn't really recommend ASI178 for deepsky, it has tiny sensor with tiny pixels. In that regard I think that ASI294 is much better way to go, I know it's more expensive but it has much bigger sensor, pixels and resolution. If you look at the comparison of the two, the 294MC Pro is the winner https://compare.astronomy-imaging-camera.com/

About the filter size, you don't need 2'' filter, your optics aren't that fast to get any vignetting with 1.25'' filter. Just get 1.25'' adapter to the telescope and use the smaller filter and the money you save up on the filter use for the better ASI camera ?

The best camera for you is often the one you can afford, I would think that if he is struggling to afford a 12nm 2inch Ha filter and a 178mc cool the ASI294mc pro is going to be well out of his budget. Its over 400 pounds more than the 178. 

He will be able to produce some great images with the 178mm-c. 

Adam

[vlaiv]

8 minutes ago, Adam J said:

The best camera for you is often the one you can afford, I would think that if he is struggling to afford a 12nm 2inch Ha filter and a 178mc cool the ASI294mc pro is going to be well out of his budget. Its over 400 pounds more than the 178. 

He will be able to produce some great images with the 178mm-c.  

Adam

Indeed, I've got ASI178mcc, and here are some examples of images with it that I took:

And

Might not be the best out there and I would certainly process them differently now, but I remember having great fun while taking these and processing them. They were taken with 80mm scope with effective FL of 384mm (or so).

I suspect one can go much deeper in dark skies as above were taken in red zone bordering with white (mag 18.5 skies).

[Adam J]

18 minutes ago, vlaiv said:

Might not be the best out there and I would certainly process them differently now, but I remember having great fun while taking these and processing them. They were taken with 80mm scope with effective FL of 384mm (or so).

I suspect one can go much deeper in dark skies as above were taken in red zone bordering with white (mag 18.5 skies).

Very nice, from a white zone you say, and with the OSC! Am impressed. 

I am still thinking he is much better of with the mono version, perticually as its cheaper as  I am guessing that under those conditions the Mono version would have done even better with the ability to add lum. 

I am guessing that the image of M101 is cropped as when I was just messing about on Field of view simulator I got a much wider field at that focal length?

Adam 

[vlaiv]

1 minute ago, Adam J said:

Very nice, from a white zone you say, and with the OSC! Am impressed. 

I am still thinking he is much better of with the mono version, perticually as its cheaper as  I am guessing that under those conditions the Mono version would have done even better with the ability to add lum. 

I am guessing that the image of M101 is cropped as when I was just messing about on Field of view simulator I got a much wider field at that focal length?

Adam 

I agree about mono version, being cheaper and more suitable for Ha but it does command an overhead in expenses for additional RGB filters and some way of exchanging them (like filter wheel, or filter drawer), although simple adapter can provide mounting for filters as a cheap alternative - but it means taking camera of scope each time filters are changed.

M101 is probably cropped, can't remember now if I did it on purpose. Field is flat over such small sensor, so I had no reason to crop it because of artifacts, but I do remember that image was taken on two separate nights - about 8h total exposure (2x 4hours) - and I did not plate solve at the time, so it might as well be due to poor alignment on consecutive nights.

[Adam J]

13 minutes ago, vlaiv said:

I agree about mono version, being cheaper and more suitable for Ha but it does command an overhead in expenses for additional RGB filters and some way of exchanging them (like filter wheel, or filter drawer), although simple adapter can provide mounting for filters as a cheap alternative - but it means taking camera of scope each time filters are changed.

Yes, but if you are buying a Ha filter anyway....and I recently saw a 5 position manual wheel sell second hand for 20 pounds on astrobuysell and a cheep set of LRGB for 40 pounds. It would depend on exactly how critical his budget is. 

In terms of processing complexity then you are going to have to combine channels anyway if he intends to use Ha luminance. 

Adam

[RolandKol]

I would go for a second hand mono setup if funds are tight.... 
Especially if funds are tight...  and if shooting will mostly be done from the city...

after year or two, you will want to try Mono as Light Pollution will be the main issue... And you will end up spending more in the long run...

However, I never seen LRGB filters for £40 in total... £40 each, yes... -  maybe...
 

[TheMan]

7 hours ago, Adam J said:

If you want to do that then you would be so so much better off picking the ZWO ASI178mm-c (mono sensor) its even cheaper than the color camera on FLO right now so there can be no excuse at all not to get it.

 

Over here in Australia they run for the exact same price. I was thinking of going for the colour sensor so I don't have to buy anything straight away and possibly save a bit of money.

[Adam J]

4 hours ago, RolandKol said:

I would go for a second hand mono setup if funds are tight.... 
Especially if funds are tight...  and if shooting will mostly be done from the city...

after year or two, you will want to try Mono as Light Pollution will be the main issue... And you will end up spending more in the long run...

However, I never seen LRGB filters for £40 in total... £40 each, yes... -  maybe...
 

Lol well they say seeing is believing dont they:

https://www.astrobuysell.com/uk/propview.php?view=143999

I did not say a premium set.

In this case a friend of mine sold these, I used them for a while before getting a premium set, however, despite being cheap I can tell you that I got better results using them and a mono camera than I had previously managed from an OSC. They are not para-focal and dont have as high a transmission as a premium set but they are perfectly capable of producing good images. 

Adam J

[Adam J]

36 minutes ago, TheMan said:

Over here in Australia they run for the exact same price. I was thinking of going for the colour sensor so I don't have to buy anything straight away and possibly save a bit of money.

I think that going for a OSC will just result in you wanting to upgrade much faster than the mono such is the difference in performance. I am glad at least that you intend to go with a cooled camera given your local temperatures.

Having been to Aus I think am aware that you have some very darks skys and so assuming you are not wanting to image in a city center then you will do better with an OSC than most.....but you will do even better still with a mono setup and if you are going to go with a Ha filter off the bat anyway you we are not talking about allot more cash.

As above there is always the second hand marked too, but that can be hit and miss.

Adam

[RolandKol]

2 hours ago, Adam J said:

Lol well they say seeing is believing dont they:

https://www.astrobuysell.com/uk/propview.php?view=143999

I did not say a premium set.

In this case a friend of mine sold these, I used them for a while before getting a premium set, however, despite being cheap I can tell you that I got better results using them and a mono camera than I had previously managed from an OSC. They are not para-focal and dont have as high a transmission as a premium set but they are perfectly capable of producing good images. 

Adam J

It looks like I missed a good deal!!!!

[Adam J]

36 minutes ago, RolandKol said:

It looks like I missed a good deal!!!!

Dont mistake them for the premium baader filters, but its a great price for what they are.