Refractor + Barlow + dslr = planets?

[TiffsAndAstro]

Been reading some interesting posts on here about using a Barlow on my 72ed with a dslr to image planets.

I assumed a Barlow lens was very similar to a Tele converter/whatever canons stupid name is,  and so 'bad' for astrophotography. Seems this is not the case?

How would I include a Barlow in my image train to try this? Would I need a specific size/thread/adapter? If it went between focus tube and flattener my back focus would stay same?

Also if it's possible, please point out any incredibly obvious potential issues I will be completely ignorant of.

I'm struggling to Google Barlow dslr planets and get anything that shows how to connect it.

[happy-kat]

planets are tiny you may not need a flattener

if you were using a tmount with a tring to your dslr then you could insert the tmount into a barlow or screw it to a shorty barlow then put dslr with barlow into focuser on telescope i think

could look at this

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

Edited April 23 by happy-kat

[TiffsAndAstro]

40 minutes ago, happy-kat said:

planets are tiny you may not need a flattener

if you were using a tmount with a tring to your dslr then you could insert the tmount into a barlow or screw it to a shorty barlow then put dslr with barlow into focuser on telescope i think

could look at this

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

I'm expecting them to be tiny but was reading a post on here from someone with same scope and the results looked good to me.

Was just thinking on a 50% cloudy evening but I can see Jupiter or Saturn it'd be pretty cool

Just have no idea size/type/fixing of the Barlow needed. There's a lot on eBay

not read all the link but first image would be pretty incredible to get. Similar camera as me, likely bigger telescope Ty for this

Edited April 23 by TiffsAndAstro

[bosun21]

You don't need a flattener for planetary imaging as you are capturing on axis images. You would fit the barlow into the focuser and then the camera. What is the pixel size of your DSLR to determine what strength of barlow would be best? The resolution of the planet won't be great though due to the small aperture of 72mm.

[Elp]

It's possible to do planetary with a DSLR but you are usually hindered by some factors:

1. The dslr sensor is quite large, so planets will appear tiny, it's one of the reasons to use a Barlow and to increase the f ratio. 

2. Image capture can be slow, for planetary you need fast frame rate due to fighting the atmospheric seeing and DSLRs even at constant image capture usually cannot capture fast enough due to large file sizes and buffers which fill up very quickly. A workaround is to use video capture as you're typically "imaging" at 25fps or faster if you have adjustable shutter speed during video capture, this can also be an issue as most cameras capture video in compressed format, using a computer controller you can possibly bypass this and capture raw video.

3. Due to 1+2 focusing can be an issue.

The connection you'd use is the usual 1.25 inch visual back of scope > barlow > t nose piece > t ring > camera.

Some eyepieces have male m42 threads under the rubber eyecup which you can screw the t ring directly onto but they are few rather than the rule.

With planetary cameras you can decrease the FOV of the cameras resolution (also called ROI or region of interest), this serves two purposes, keeping files sizes per image smaller and increasing the FPS of the camera capture rate if the camera is capable of it (I've done over 100FPS at times with a camera that can theoretically do 150, you then get into storage bandwidth issues (memory not being fast enough to keep sustained write speeds) and your storage space filling up incredibly quickly, a typical session I capture 20-30Gb of image files in around 30 mins of being outside on one planet).

Edited April 23 by Elp

[900SL]

Some relevant stuff here. 

 

[michael8554]

1. Is it a Canon DSLR, you didn't say ?

Shoot Canon video this way:

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

2. It doesn't matter much that planets appear as "dots" in DSLR images.

If you crop the eg 5000 x 3000 pixel images to a typical planetary camera image size of 1280 x 1024.

Hey, the planet looks the same size as if you'd shot with a planetary camera !

Also it's much easier to place that tiny dot on a DSLR sensor than in a tiny sensor Planetary camera .

3. 420mm focal length is pretty short for Planetary, even with Barlowing.

Many are using a 2000mm FL SCT and Barlowing !

Michael

 

[WolfieGlos]

I assume you are talking about this thread ?

If so, as michael has referred, just know the limitations and don't expect the incredible images you see taken with large SCT's and Dobs.

A picture says a 1000 words, so to give you an idea, the following links are to images with my Starfield 102ED refractor + 2x barlow + ASI-585MC. Jupiter and Saturn , Jupiter with Ganymede shadow animation . Remember that that's nearly double the focal length of your 72ED and, crucially, using a high-speed planetary camera. The effective focal length was around 1500mm if I recall correctly, and the ROI reduced to increase frame rate. I've not tried it with a DSLR.

Here is my rig I used to image the Moon with the 72ED from indoors, and I note I stated I didn't have enough focuser travel to achieve focus with a barlow. And here is my 102 ED. The barlow is a 1.25" nose piece fit, and both scopes come with a 1.25" clamp fit.

Planetary imaging is completely different to DSO imaging; this superb FAQ over on CN helped me a lot in getting started. Pay particular attention to section 6 to establish the best barlow length to suit your scope, camera and seeing conditions.

Presently, most of the planets aren't visible. Take a look in the Planetary imaging section too; you won't find many posts being made now, but it is a hive of activity during the season.

Hope that helps.

Edited April 24 by WolfieGlos

[TiffsAndAstro]

Ty all for this need to have a detailed read.

I thought maybe I could use a Barlow, screw it all together in image train and get (eg) 1000mm and f12 ish. The low f wouldn't matter planets are bright.

As usual seems not. But need to read all the above in detail first. 

Ty again

[900SL]

I've shot the moon with a 90mm f6, barlow and a small pixel camera (178MM). It can be done. Requires fast frame rate video and autostakkert etc 

Jupiter and Saturn require longer focal lengths

 

 

Edited April 25 by 900SL

[johnturley]

On 23/04/2024 at 14:41, happy-kat said:

planets are tiny you may not need a flattener

 

You definitely will not need a flattener.

John 

[TiffsAndAstro]

20 minutes ago, johnturley said:

You definitely will not need a flattener.

John 

at least i have a flattener

[TiffsAndAstro]

On 23/04/2024 at 15:58, bosun21 said:

You don't need a flattener for planetary imaging as you are capturing on axis images. You would fit the barlow into the focuser and then the camera. What is the pixel size of your DSLR to determine what strength of barlow would be best? The resolution of the planet won't be great though due to the small aperture of 72mm.

im gonna go look at astro tools see how big saturn and jupiter seem in my fov.

i have a 600d 4.29 pizel size

even with a 5x barlow, jupiter looks about 2 x 2 pixels in astronomy tools  

Edited April 25 by TiffsAndAstro

[TiffsAndAstro]

1 hour ago, 900SL said:

I've shot the moon with a 90mm f6, barlow and a small pixel camera (178MM). It can be done. Requires fast frame rate video and autostakkert etc 

Jupiter and Saturn require longer focal lengths

 

 

i actually thought the moon a pretty dull target to image, but your images are nothing short of amazing. 

[900SL]

33 minutes ago, TiffsAndAstro said:

i actually thought the moon a pretty dull target to image, but your images are nothing short of amazing. 

Thanks! That was beginners luck. I think seeing must have been pretty good that evening, struggled to match it since.

From memory your barlowed focal ratio should be 4x to 5x your pixel size. So for my 2.4 micron camera, f12 is a nice ratio, which is 2x barlow and f6 scope. The resolution of the 90mm scope supports that as well.

For my 3.75 micron cameras, f15 to f18. This means 3x barlow, and is very seeing dependant 

Good lunar requires pin sharp focus. Use the nask on a bright star or planet. Video with short exposures and reduced frame size for fast frame rate. I don't shoot using the full sensor, but use a smaller region. You can do this with a dedicated astrocam, not so with a dslr from memory

[TiffsAndAstro]

5 minutes ago, 900SL said:

Thanks! That was beginners luck. I think seeing must have been pretty good that evening, struggled to match it since.

From memory your barlowed focal ratio should be 4x to 5x your pixel size. So for my 2.4 micron camera, f12 is a nice ratio, which is 2x barlow and f6 scope. The resolution of the 90mm scope supports that as well.

For my 3.75 micron cameras, f15 to f18. This means 3x barlow, and is very seeing dependant 

Good lunar requires pin sharp focus. Use the nask on a bright star or planet. Video with short exposures and reduced frame size for fast frame rate. I don't shoot using the full sensor, but use a smaller region. You can do this with a dedicated astrocam, not so with a dslr from memory

Ty for this but I have a lot more reading to do before attempting this side project.

Maybe when I run out of galaxies

[Elp]

To be honest I'd just go out and do it, no amount of reading makes up for hands on experience. I've never read into the technicalities of any of it.

It is however not a good time to image the planets at this moment in time, they're too low or set early/rise in the morning.

Edited April 25 by Elp

[TiffsAndAstro]

2 minutes ago, Elp said:

To be honest I'd just go out and do it, no amount of reading makes up for hands on experience. I've never read into the technicalities of any of it.

It is however not a good time to image the planets at this moment in time, they're too low or set early/rise in the morning.

yeah i agree, but before i do i need to make sure i buy the correct bits and peices that will work first time for my gear. jupiter is visible for a little while after dark from where i am, but for now im gonna try and concentrate on maximising hours on something. Until june ish, when i think stellarium is telling me m31 is back.

ngc4889 "thousand galaxies" is interesting atm. who wouldn't want a pic containing 1000 galaxies?

[Elp]

If you've got the equipment at hand you'll generally get a result, I did it on my first attempt with a 60mm refractor, barlow, but I was using a 224mc camera, its a popular plantery camera and doesn't cost much, in fact it's very cheap now compared to its original price.

[900SL]

One thing to watch.. with a barlow/dslr imaging set up you may need an extension tube if you remove the flattener/reducer, otherwise you might not get focus. I needed around 80mm extension after the focuser