Curious about dslr imaging with a barlow

[col]

Hi guys

I'm a visual astronomer normally, but playing around with my astro stuff I found the 2x Barlow would screw on to my dslr and wondered what difference it makes. 

My reason for asking is I put my dslr onto the focus tube of my startravel 102 and the image in the the dslr's screen of Saturn was barely a dot,only seeable if I used the cameras digital zoom. Which reverts back to a dot when taking a picture of it. 

Does a 2x Barlow increase that so saturn can be seen more than just a dot, or is my ignorance with Astro photography showing? 

Cheers all. 

 

 

[Steve Ward]

Yes , it'll give you a very slightly bigger dot with your DSLR .

[col]

2 minutes ago, Steve Ward said:

Yes , it'll give you a very slightly bigger dot with your DSLR .

Thanks for that, I was hoping it would be better than a bigger dot though. 😁

 

[Steve Ward]

You're a visual observer ... you know the difference in view when you add the Barlow to an eyepiece , nothing different when adding it to a camera.

[col]

34 minutes ago, Steve Ward said:

You're a visual observer ... you know the difference in view when you add the Barlow to an eyepiece , nothing different when adding it to a camera.

Cheers Steve, 

Yes I didn't think, I don't know anything about AP so wondered if there was something different happening with the cameras possibly. 

I'll stick with visual and maybe try the phone the odd time at the eyepeice. 

[happy-kat]

Depending on what DSLR you have you might find this useful

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

[johnturley]

With a DSLR in order to get decent sized planetary images you will probably need to use eyepiece projection, as a Barlow will generally not provide sufficient amplification for the size of sensor in a DSLR, but they work fine for the smaller sized sensors you get with dedicated planetary cameras.

Eyepiece projection tubes (in which you could fit an eyepiece of your choice) were quite commonplace at one time, but you don't see them advertised much nowadays, alternatively Baader offer adaptors to fit their Hyperion and Morpheus range of eyepieces to enable eyepiece projection.

John  

[col]

1 hour ago, happy-kat said:

Depending on what DSLR you have you might find this useful

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

Thanks Happy-Cat

Mine is a Nikon 3200, so not on the list of cameras in the link. 

[col]

49 minutes ago, johnturley said:

With a DSLR in order to get decent sized planetary images you will probably need to use eyepiece projection, as a Barlow will generally not provide sufficient amplification for the size of sensor in a DSLR, but they work fine for the smaller sized sensors you get with dedicated planetary cameras.

Eyepiece projection tubes (in which you could fit an eyepiece of your choice) were quite commonplace at one time, but you don't see them advertised much nowadays, alternatively Baader offer adaptors to fit their Hyperion and Morpheus range of eyepieces to enable eyepiece projection.

John  

And thanks too John

I was just curious if mine would work simply with the Barlow, as its things I had to hand, so thought I would have a go if it did work. 

I'm not into AP enough to start getting adapters ect. 

[michael8554]

Don't worry too much about the Barlowed image only being a "dot".

Whether you use a large-chip DSLR, or a tiny-chip Planetary camera, the image size on the chip is the same.

The Planetary camera isn't magically producing a larger image.

By the time you've cropped the DSLR image it will be a similar pixel width and height as a planetary camera's output.

Michael

 

[johnturley]

2 hours ago, michael8554 said:

Don't worry too much about the Barlowed image only being a "dot".

Whether you use a large-chip DSLR, or a tiny-chip Planetary camera, the image size on the chip is the same.

The Planetary camera isn't magically producing a larger image.

By the time you've cropped the DSLR image it will be a similar pixel width and height as a planetary camera's output.

Michael

 

I'm surprised about your comment, as its contrary to what a number of people have posted previously, one of the reasons I bought a planetary camera was because with a digital SLR the image scale was far too small unless I used eyepiece projection.

I found that I couldn't do anything much with the resultant tiny images in processing programs such as Registax and Lightroom.

Also if the image is just a dot on the DSLR screen, it will be difficult to achieve correct focus.

John

Edited August 20, 2022 by johnturley

[michael8554]

"one of the reasons I bought a planetary camera was because with a digital SLR the image scale was far too small"

A planetary camera with the same size pixels as a DSLR will have exactly the same image scale.

For instance, 2000D 3.72um,  ASI 120MM 3.75um.

With your 500mm FL scope the image scale of both is approximately 0.75arcsec/pixel Barlowed, 1.50arcsec/pixel without.

Perhaps you mean the FOV was too large ?

But as I said, crop the DSLR and you have the same size image in pixel width and height as the planetary cam.

"Also if the image is just a dot on the DSLR screen, it will be difficult to achieve correct focus."

Agreed.

You can try the 10X mag on LiveView, or attach to a laptop which will have a much larger display.

Michael.

[vlaiv]

Two things really limit DSLR usability as planetary camera.

First is ability to crop sensor to smaller size when shooting video.

Second is ability to record raw video.

If DSLR can do these two things, then it is not different to planetary camera. Most DSLRs can't do that.

If you for example have 6000x4000px sensor and you shoot 1920x1080 video - that does not mean it has been cropped! It is still same FOV that has been binned / resampled in video - which changes effective pixel size.

Another issue is compression in video recording. Most DSLRs shoot mp4 video. Compression messes up detail in recording and you want raw video without compression (at least not lossy compression).

If you want to get decent planetary images - then planetary camera, or even modified web camera will be better choice (for web cam - same things apply - need to be able to record raw and to crop).

 

[col]

Theres a lot more to AP than I'm interested in trying, but I will try the Barlow connected to the dslr just out of curiosity of what it might show. 

But thanks for all the views and advice guys, but I'll mainly stick to visual as there's nothing more relaxing than just enjoying the view. 

But curiosity has struck 😁 so I'll try with this simple set up and will let you know how I get on. 

[michael8554]

Vliav

Happy-kat's link addresses many of your DSLR video objections:

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

Michael

[vlaiv]

9 minutes ago, michael8554 said:

Vliav

Happy-kat's link addresses many of your DSLR video objections:

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

Michael

I'm a bit confused by that page as it does not mention anything about raw video being recorded. It mentions MOV video format which is mostly mp4 compressed.

Have you tried recording with DSLR like that? What sort of file size do you get?

For reference, 60fps, 640x480px at 8bit - one minute raw video would end up being about 1.03GB of data.

 

[johnturley]

I think that we can safely say that although you can produce some reasonable planetary images from a digital SLR, they will never be as good as what can be achieved with a dedicated planetary camera.

The attached image of Mars in 2020 was taken through my 14in Newtonian using eyepiece projection with a 9.7 mm Plossl eyepiece, not bad maybe, but nothing like what can be achieved with a dedicated planetary camera. 

I still maintain that there isn't a satisfactory method of producing a decent sized image from the small image you will if get if just using a Barlow to enlarge the image with a full frame, or standard crop frame digital SLR. 

John 

 

Edited August 21, 2022 by johnturley