10 replies to this topic

[ro311974]

Hi everybody,

 

I am new to the astro hobby so I am just about to build my first rig and I want to start small, so for now I want to get Sigma lenses for my Canon EOS rebel T7 https://www.bhphotov...1_4_dg_hsm.html but I am curious is any of those extenders (listed below) work with my camera and the Sigma lenses?

From the list it doesn't look like it but I just want to double check:

 

https://www.bhphotov...I.html/overview

https://www.bhphotov...r.html/overview

 

Best regards,

Rob

 

[Son of Norway]

I can't answer your question. But from my own experience, I have a 70-300 mm lens that I use with my Canon 650D.  It is all the lens that my SkyGuider Pro can handle and all the lens I need for the the widefield targets that I want to capture. I haven't extended it to 300mm yet.  A tele-extender would not give me any added benefit.

[ro311974]

Thanks. Also - do I need a guiding cam for that mount to do the 3 star polar allingnment or my Sigma lenses will be enough?

[SpaceMax]

Hi Ro, not sure what mount you have but the polar alignment routine is generally performed visually. The alignment could be done with the main camera and whatever lens but given the likely short focal length your accuracy maybe somewhat off. It will still perform goto if your mount has that in build. If your mount has no goto, say it’s a SkyGuider Pro or similar, there will be no 3 star alignment routine to perform.
Polar alignment is best done with a pole scope or via a dedicated camera such as the polemaster. But if you are on the northern hemisphere you should have no issues finding Polaris provided you have a clear view north.

As for focal extenders, they inevitably add glass to your imaging train as well as an increase in glass to air transitions, which usually gives rise to amplified optical flaws and imaging rendering. They also increase your f/ratio and with it exposure length requirements. Longer focal length also means higher demands on polar alignment and tracking accuracy.
Many objects in the nearby cosmos are rather large and fit well between 70 and 150mm focal length on a full frame, so if you bring a 50mm and a 100mm and both in f2.8 you can shoot for years. Wouldn’t recommend teleextenders or Barlows for imaging.

Clear Skies!
Max

[ro311974]

Thanks for all the answers guys - much appreciated

I have another question: I just sent back second eqm 35 pro because of it's polar scope not being calibrated. I am willing to give a try to a lighter mount, probably Sky-Watcher Star Adventurer GTi but I was wondering - why the polar scope is not calibrated properly from the get go. I mean, realize that this hobby requires a bit of DIY but for almost 800 or 900 bucks I think I can, and I should,  expect the polar scope to be calibrated, no? 

I tried to calibrate it with my first eqm35 mount and it was a major disaster - there are like 20 youtube videos that show how to do it but they all have a bit different approach, not to mention that the polar calibration is not even mentioned in the eqm 35 manual. I needed to download the GTi manual to check. My first attempt ended up with mowing the screws too much and the reticle fell off and I needed to place it back again. 

For a while I was thinking maybe I can get the LIGHTRACK II MOUNT (since for now I decided to go with the Rokinon 135 mm f/2 with my Canon Eos Rebel T7, which will give me around 200 mm on a crop sensor - seems to be a good choice as a starter) but I have seen that the polar aligment scope is even worse than in the sky watchers. I really thought the Lighttrack would be perfect for me. 

Edited by ro311974, 12 April 2024 - 09:12 PM.

[bignerdguy]

Hi everybody,

 

I am new to the astro hobby so I am just about to build my first rig and I want to start small, so for now I want to get Sigma lenses for my Canon EOS rebel T7 https://www.bhphotov...1_4_dg_hsm.html but I am curious is any of those extenders (listed below) work with my camera and the Sigma lenses?

From the list it doesn't look like it but I just want to double check:

 

https://www.bhphotov...I.html/overview

https://www.bhphotov...r.html/overview

 

Best regards,

Rob

The first link says the following:

"The Extender EF 2X III from Canon is designed for select Canon EF mount L-series telephoto lenses"

And the second says:

"Optimized for Canon EF-mount lenses in the Global Vision line"

 

So no, they wont work for Sigma Lenses.  They are for the ES line from Canon or L line depending on the model.  the second link also has a list of compatible lenses.

 

 

Thanks for all the answers guys - much appreciated

I have another question: I just sent back second eqm 35 pro because of it's polar scope not being calibrated. I am willing to give a try to a lighter mount, probably Sky-Watcher Star Adventurer GTi but I was wondering - why the polar scope is not calibrated properly from the get go. I mean, realize that this hobby requires a bit of DIY but for almost 800 or 900 bucks I think I can, and I should,  expect the polar scope to be calibrated,

No, due to shipping and other issues the manufacturers rarely align the polar scopes fully.  they do a quick align at the factory but during shipping things tend to get moved around a bit and will cause the scopes to be off as a result. it is even in most manuals that you would need to align the scope to the mount.  a solution is there are polar cameras that are designed to eliminate the need for a scope and do the hard part for you.  All you need to do is plug them in, attach them to the polar scope end and then follow instructions on a computer to properly align your mount.  They are kinda pricy but if you can afford it might be worth it...

[archer1960]

Hi everybody,

 

I am new to the astro hobby so I am just about to build my first rig and I want to start small, so for now I want to get Sigma lenses for my Canon EOS rebel T7 https://www.bhphotov...1_4_dg_hsm.html but I am curious is any of those extenders (listed below) work with my camera and the Sigma lenses?

From the list it doesn't look like it but I just want to double check:

 

https://www.bhphotov...I.html/overview

https://www.bhphotov...r.html/overview

 

Best regards,

Rob

If you want a Tele-extender (which you probably don't to start), get one from Sigma that they say will work with the lens you are buying. Theoretically any tele-extender should work with any lens, but IME that is rarely the case.

[ro311974]

Thank you for all your answers  

[rising1]

If you want a Tele-extender (which you probably don't to start), get one from Sigma that they say will work with the lens you are buying. Theoretically any tele-extender should work with any lens, but IME that is rarely the case.

A matched teleconverter is probably a good idea, but it is not true that any teleconverter will work with any lens (of the same mount). There are cases where the teleconverter will collide with the rear element of a lens it was not designed for. I think third party teleconverters such as Kenko generally don't have this issue.

 

In any case teleconverters (especially 2x) are a mixed blessing and probably only useful on high quality lenses.

[bignerdguy]

Also forgot to mention, if you want a teleconverter that is specific to the Sigma lenses, try this search link on Amazon.  there are quite a few though they are pricey.

 

https://www.amazon.c...&ref=nb_sb_noss

[Colorado DSLR Photographer]

Based on my several decades daytime experience with tele extenders and the often diminished sharpness, and loss of light via f/stops, at least for myself I can say I would not even consider using a tele extender over a longer focal length lens, or a designated astrograph refractor like the William Optics Red Cat Series an option for any kind of astrophotography. Except for the proprietary Canon tele extenders I used on my 400mm, 600mm, and 800mm L glass for wildlife shots  I can honestly say that I have never been satisfied by the end results of all the other tele extenders/tele converters I have tried; and in my most recent sell off of not used equipment to KEH there actually were five of those contraptions from Kenko, to Sigma, and Tamron, all in EF-mount, all used only once, or twice.