Planetary Imaging with DSLR and Barlow

[MessierMatt]

Hi all,

I am very new to visual and AP and keen to learn from any advice. I have a super basic set up and am keen for some pointers around planetary photography using a 5inch 750mm reflector and a DSLR (Canon 800D). I understand that a dedicated planetary camera is better suited due to the smaller sensor size but was wondering if I should be using a 2x, 3x or 5x Barlow for planets. I currently have a stock 2x Barlow and am willing to spend approx £100 to upgrade this. 
Has anyone got any experience of this or specific advice?

Am I better using eyepiece projection?

[Mr Spock]

This was taken with a 100mm f7.4 (740mm) refractor with a x2 Barlow on a Nikon D500, with a slight crop, to give you some idea of the scale.

[MessierMatt]

2 hours ago, Mr Spock said:

This was taken with a 100mm f7.4 (740mm) refractor with a x2 Barlow on a Nikon D500, with a slight crop, to give you some idea of the scale.

Beautiful image. The 2x works well on the moon. Lovely details.

I am thinking that a higher power Barlow would allow more info to hit the pixels of the sensor giving more details on, for example Saturn or Jupiter. So when cropped, there would be more data. Is this correct? I know that there would be a large loss of light and therefore I would have to use a higher iso/longer exposure. 

[Elp]

Though it's possible, DSLRs aren't suited for planetary as you say one the main issues is that their sensors are large, if you look at astronomy.tools website you can see for yourself if you input your setup numbers even if that fov calculator is just a guide, a large planet like Jupiter will look tiny so the sensor won't be capturing any detail.

Your second problem with planetary is atmospheric conditions on earth or where you are. If you look visually via an eyepiece you can see this yourself, the target will appear to wobble come into focus suddenly then blur, this is atmospheric seeing at play. Good planetary images are made via hundreds/thousands of images captured per session within a space of a minute or a handful of minutes, then sorted via software like autostakkert then only a minor percentage of the best frames are used and stacked. A DSLR is not capable of capturing quick enough and at a constant rate, even whilst in video mode, hence why planetary cameras are used. Longer exposure, that doesn't work on planetary, you'll just get a smudge of pixels.

You can try with a Barlow but I believe you'll be causing more issues, such as the increased focal ratio therefore "dimming" the amount of light getting to the camera sensor. Having tried a few barlows myself, I wouldn't go over 2x, maybe 3x at the absolute limit. 5x, forget it.

Your best chance is eyepiece projection and if you persevere by taking lots of images you may get one just in focus when the seeing is settled. Some eyepieces have a thread on the eyecup end allowing connection via a t ring adaptor.

Edited May 5, 2023 by Elp

[MessierMatt]

1 minute ago, Elp said:

Though it's possible, DSLRs aren't suited for planetary as you say one the main issues is that their sensors are large, if you look at astronomy.tools website you can see for yourself if you input your setup numbers even if that fov calculator is just a guide, a large planet like Jupiter will look tiny so the sensor won't be capturing any detail.

Your second problem with planetary is atmospheric conditions on earth or where you are. If you look visually via an eyepiece you can see this yourself, the target will appear to wobble come into focus suddenly then blur, this is atmospheric seeing at play. Good planetary images are made via hundreds/thousands of images captured per session within a space of a minute or a handful of minutes, then sorted via software like autostakkert then only a minor percentage of the best frames are used and stacked. A DSLR is not capable of capturing quick enough and at a constant rate, even whilst in video mode, hence why planetary cameras are used. Longer exposure, that doesn't work on planetary, you'll just get a smudge of pixels.

You can try with a Barlow but I believe you'll be causing more issues, such as the increased focal ratio therefore "dimming" the amount of light getting to the camera sensor. Having tried a few barlows myself, I wouldn't go over 2x, maybe 3x at the absolute limit. 5x, forget it.

Your best chance is eyepiece projection and if you persevere by taking lots of images you may get one just in focus when the seeing is settled.

Thanks for this @Elp really clear advice.  I will have a go at some EP projection.

[michael8554]

Hi Matt

"a dedicated planetary camera is better suited due to the smaller sensor size".

Dedicated planetary cameras are preferred because they provide high framerate uncompressed video.

The sensor size doesn't matter, so long as it's larger than the focused image.

"DSLRs aren't suited for planetary as you say one the main issues is that their sensors are large,........................ a large planet like Jupiter will look tiny so the sensor won't be capturing any detail."

Lets compare a planetary camera with 3.75um pixels, and a DSLR with 3.75um pixels.

Crop the DSLR image to the same size as the planetary camera's sensor, you end up with two identical images with the same resolution.

In fact that's one way you can use your DSLR to do planetary, using Liveview 5x Video mode, or Crop Video mode:

https://www.astropix.com/html/equipment/canon_one_to_one_pixel_resolution.html

The main advantage of a DSLR is that finding the planet with the large sensor is so much easier than trying to "thread the needle" with a tiny 1/3" sensor.

Michael

 

[Cosmic Geoff]

You need to make some attempt to match the effective focal ratio to the pixel size of the camera.  This means that with larger pixel sizes and fast telescopes you need a Barlow.  The newer dedicated planetary cameras often have 2.9um pixels which will match with a f10 SCT without requiring a Barlow lens.

In practice a dedicated planetary camera is likely to be  easier to use and offer a higher video frame rate than a DSLR.  

[MessierMatt]

3 hours ago, michael8554 said:

Hi Matt

"a dedicated planetary camera is better suited due to the smaller sensor size".

Dedicated planetary cameras are preferred because they provide high framerate uncompressed video.

The sensor size doesn't matter, so long as it's larger than the focused image.

"DSLRs aren't suited for planetary as you say one the main issues is that their sensors are large,........................ a large planet like Jupiter will look tiny so the sensor won't be capturing any detail."

Lets compare a planetary camera with 3.75um pixels, and a DSLR with 3.75um pixels.

Crop the DSLR image to the same size as the planetary camera's sensor, you end up with two identical images with the same resolution.

In fact that's one way you can use your DSLR to do planetary, using Liveview 5x Video mode, or Crop Video mode:

https://www.astropix.com/html/equipment/canon_one_to_one_pixel_resolution.html

The main advantage of a DSLR is that finding the planet with the large sensor is so much easier than trying to "thread the needle" with a tiny 1/3" sensor.

Michael

 

Thanks @michael8554 . So actually trying to image planets by using a Barlow and dslr is not recommended and therefore buying an upgraded Barlow or x3 is not needed as through capturing the live x5 video feed is more effective. I’ve read a few articles on this and am aware I need dedicated software and a laptop linked to the camera. 
I was under the impression that by using a x3 Barlow the planet image would hit more pixels on the dslr sensor hence improving details. Is this the case?

thanks for taking the time to respond. I really appreciate everyone’s responses. 

[michael8554]

Hi Matt

"So actually trying to image planets by using a Barlow and dslr is not recommended "

That's not what I meant to imply.

A planetary camera will be best, but your DSLR can be used to good effect, if budget is tight.

A x2 to x5 Barlow or Powermate will help, but there comes a point with any scope where too much "magnification" actually degrades the image.

Michael