Will this vignette?

[parallaxerr]

I'm planning on purchasing a Canon 550D for planetary imaging with my 150MAK. For a few reasons I would like to stick with a 1.25" nosepiece, mainly so that I can use my 1.25" micro-focuser and also to keep the cost down on a UV/IR cut filter.

The question is, will I experience any vignetting with this setup? 

POINT TO NOTE - the camera will be operating in movie crop mode, so 640x480 pixels. For this reason, I think it will be OK, but I am not 100% sure.

TIA, Jon

[tomato]

I’ve plugged your scope and camera into the FLO imaging FOV tool. Based on this for planetary imaging, even if you have severe vignetting going on, this would crop out?

[parallaxerr]

Hi Tomato,

The camera will be running at 640x480 in movie crop mode, so I believe tor FoV will be more like this....

 

As you can see, any vignetting at this FoV may affect the image. However, given that this is the central ~40% of the chip by pixel area, I kind of think the 1.25" nosepiece will be OK. Just wondered if anyone had any first hand experience.

I can always try with a 1.25" and a 2" nose peiece. The 2" option just leads me down a more expensive filter route and possibly a new focuser....and I don't need much encouragement to buy one of those 😂

[tomato]

If the camera mode you are using is only using 40% of the available sensor area then I would think that would take care of any vignetting, I guess the way forward would be to try it out.

[david_taurus83]

Why not just buy a colour planetary camera in the first place? Be much better frame rate and will work no problem with 1.25" focuser.

[paul mc c]

3 hours ago, david_taurus83 said:

Why not just buy a colour planetary camera in the first place? Be much better frame rate and will work no problem with 1.25" focuser.

As David says can't compare to a dedicated planetary camera. 

[ONIKKINEN]

No vignetting, even if you obstruct 90% of the sensor somehow. The capture area is a tiny square in the middle of the sensor with no interpolation, however..

 

I have used the 550D in movie crop mode to do some planetary work and i wouldn't recommend it unless its almost free for you. Dont get me wrong, it will work and you can capture at least Jupiter with it, but there are issues. The stock movie crop mode is very noisy and i believe very compressed also. Quantum efficiency of the 550D is around 40%, so you will need to use a pretty high ISO to get signal.

 

You can install magic lantern, a third party firmware package to unlock raw video (i believe 14bit, but still noisy) to get slightly better results. You will need to limit the capture framerate to 38fps, at least i had to. Even then the camera freezes and hard crashes every now and then. You will probably lose a few recordings. If you are paying any kind of real money for it, i would recommend buying any cheap planetary camera.  Even the SVBONY 105 at 60 bucks will probably be much better than the 550D.

[parallaxerr]

On 01/10/2021 at 21:25, david_taurus83 said:

Why not just buy a colour planetary camera in the first place? Be much better frame rate and will work no problem with 1.25" focuser.

 

On 02/10/2021 at 00:34, paul mc c said:

As David says can't compare to a dedicated planetary camera. 

The reason for choosing the DSLR is because I don't have a laptop to run a planetary camera. Nor, to be honest, do I have any other reason to own a laptop so by the time the cost of one is added in, the DSLR becomes the cheaper option.

However, @ONIKKINEN has pointed out some real drawbacks that I was unaware of, thanks for the info.

More thinking time required....

[CraigT82]

You don't need to spend more than £100 on a laptop, that's what I paid on gumtree for a used lenovo thinkpad with 2x USB3 ports and a 250gb SSD.

Mind you with the current situation around supply used prices will probably be significantly higher at the minute. 

[parallaxerr]

By way of a follow up - thanks for the advice guys, I decided against the 550D.

I have revived an old laptop so a dedicated camera is on the cards, but I am concerned over the specs and performance, so I started a more specific thread to address those questions here -