camera comparison

[Fieldsy]

Hi guys I'm just looking over these 2 cams to be used with 130pds scope . Both at £300 ish .would one of you great ppl take look and put into simple terms pro/cons.

Thanks Si

[Adam J]

5 minutes ago, Fieldsy said:

Hi guys I'm just looking over these 2 cams to be used with 130pds scope . Both at £300 ish .would one of you great ppl take look and put into simple terms pro/cons.

Thanks Si

I think you forgot to mention which two cameras you are talking about. 

[Fieldsy]

Doh it’s in the tags lol

gpcam3 290m

gpcam3 178m 

leaning more to the 290 but that’s only because it’s got 5star bbc sky review

[Adam J]

1 hour ago, Fieldsy said:

Doh it’s in the tags lol

gpcam3 290m

gpcam3 178m 

As discussed in your last thread I would say that both of those cameras have very small sensors for the focal length of the 130PDS. 

As a result in either case you will be limited to imaging smaller targets. The lack of cooling will also limit you to shorter exposures to prevent thermal noise from dominating. 

Have you had a play with Field of View Simulator? 

http://www.skyatnightmagazine.com/astronomy-field-view-calculator

It will help you understand what targets will fit onto your sensor. Use the ASI178mm and the ASI290mm as the site does not have the altair cameras. 

In either case you will be specializing in imaging smaller galaxies should you chose either of those cameras using the short exposure technique.

In terms of resolution / pixel size I would say that you will not see much difference between the two cameras 2.4um vs 2.9um, so I would not see that as a deciding factor. 

That leaves it as a straight shoot out between a larger FOV in the 178 and higher sensitivity in the 290. 

You will struggle to 100% fit targets like M81 and M101 into the field of view of the 290 while as you will have no issues with the 178. The 178 has twice the sensor area and arguably a better aspect ratio.  It will also be easier to locate targets with the 178 in comparison to the 290 which will require very accurate GoTos

178 = 39.30' x 26.40' = 0.29

290 = 29.69' x 16.81' = 0.14 

Looking at sensitivity, if you assume that you want at least 10 stops of dynamic range then you get:

178 = 1.4e read noise 

290 = 1.1e read noise

By the time you take into account pixel size then you get relative sensitivities of approx:

178 = (2.4)^2 / 1.4 = 4.11

290 = (2.9)^2 / 1.1 = 7.64

Hence, discounting other noise sources due to the short exposures the 290 is about 1.9x more sensitive than the 178 meaning that your exposures will need to be about twice as long with the 178 and that means that you will be doing exposures of between 2 seconds and 5 seconds for the 290 and between 4 seconds and 10 seconds for the 178 assuming that you are using the short exposure technique to get under the seeing for maximum imaging resolution. In either case you will need 1000's of exposures to achieve good results with this technique.

The 178m has more pixels and as a result the total amount of image data that you will need to store will be about 3x that of the 290 and it will take about three times longer to stack (This may not be an issue for you depending on your PC). 

To summarise I would base the choice on the following factors:

1) Do you want to image medium size galaxies such as M101 and M81 without having framing issues? If you do then you are better of getting the 178.

2) Do you want to image some of the brighter more compact planetary nebula / SN remnants in Narrowband using longer ~60s exposures: Something like the crescent NGC6888 or the Bubble Nebula + surroundings or the Cygnus wall? All will fit better into the FOV of the 178 then it does into the 290.

3) Do you want to want to achieve the very best possible performance with the 130PDS when imaging small galaxies in high resolution at the cost of medium sized objects? Get the 290mm as its a much better choice for that specialized task. 

If I was in your position of just starting out I would want the more flexible camera and would go for a IMX178mono based camera. 

If you can get hold of it and can spend a little more the hypercam packaging has some advantages over the GPCAM3 in terms of using filters and connecting to the scope as you can space it easily from a coma corrector with only T2 adapters. With the GPCAM3 you will most likely need a converter and a filter wheel to achieve this.  

https://www.harrisontelescopes.co.uk/acatalog/altair-hypercam-imx178-usb3.0-mono.html

Also consider the ASI178mm as I am not sure that Altair have not discontinued 178m variants so you may have some issues getting hold of them. 

Note that you will most likely need a coma corrector and a method of spacing the camera 55mm to the sensor from the rear of the corrector. You could try it first without mind you as you may just get away with it. 

Adam 

 

 

 

 

 

 

 

[Adam J]

1 hour ago, Fieldsy said:

Doh it’s in the tags lol

gpcam3 290m

gpcam3 178m 

leaning more to the 290 but that’s only because it’s got 5star bbc sky review

Also there is this:

https://www.astrobuysell.com/uk/propview.php?view=147379

if you can stretch the budget it may be a more versatile camera despite its age.

Adam

[Fieldsy]

14 minutes ago, Adam J said:

Also there is this:

https://www.astrobuysell.com/uk/propview.php?view=147379

if you can stretch the budget it may be a more versatile camera despite its age.

Adam

Adam this is tough ?  well unless I get a cam I’m going to be using my qhy5 Ii so I may just get the 290 and work on smaller stuff for now then jump up properly later I’m thinking.?

what does trigger mean ?

Video exposure duration shortest/longest (Video Mode): 0.244 ms (0.000244 secs) - 5 secs
Deepsky exposure duration (Trigger Mode): 0.244 ms (0.000244 secs) - 1000 secs (16.66mins)

 

[Fieldsy]

Well I've had another read on it all and I've decided to get the asi178 mono .?? and I can jump up in a year or so .thanks Adam  for trying to simplify all the specs and making them manageable ish.

[Adam J]

1 hour ago, Fieldsy said:

Adam this is tough ?  well unless I get a cam I’m going to be using my qhy5 Ii so I may just get the 290 and work on smaller stuff for now then jump up properly later I’m thinking.?

what does trigger mean ?

Video exposure duration shortest/longest (Video Mode): 0.244 ms (0.000244 secs) - 5 secs
Deepsky exposure duration (Trigger Mode): 0.244 ms (0.000244 secs) - 1000 secs (16.66mins)

 

Like I say I would probably recommend the 178 to you for the additional field of view, worth noting that while the 290 is very very very sensitive thats not to say the 178 is rubbish in this regard. But if you really want to full specialise in small targets I understand your choice.

Those are just the exposure lengths. You would use video mode for solar system imaging and Trigger mode for deep sky imaging. You wont want ot go longer than 16.66mins.

 

[Adam J]

1 minute ago, Fieldsy said:

Well I've had another read on it all and I've decided to get the asi178 mono .?? and I can jump up in a year or so .thanks Adam  for trying to simplify all the specs and making them manageable ish.

I think that is the correct choice. When you eventually want a larger cooled camera  in the future you will have still be able to use the 178 as a excellent guide and solar system imaging camera. So no downsides to starting with that camera.

[cletrac1922]

Adam

Tks for that

I was looking at the 290 mini and the 178 as well for imaging, with my ED80, on a EQ5 mount

John

 

[Adam J]

3 hours ago, cletrac1922 said:

Adam

Tks for that

I was looking at the 290 mini and the 178 as well for imaging, with my ED80, on a EQ5 mount

John

 

As above, if you can afford a cooled camera then its worth the extra. I would also say that if you can afford the 183 mono, even uncooled then that is a better option as it will allow for larger targets.

In the end though as above if you have a 300 pound budget and dont want to save for longer, then you have a 300 pound budget.

Adam