Show me your lenses for your nexstar 6SE

[icebergahed]

Hi

I am intrested in what lenses people have for this scope, as i am currently upgrading mine. Im using the f6.3 reducer that i dont think i will be taking off regularly so will calculate my magnifications from that.

More pics the better, as im currently struggling to understand the big visual quality difference between a £100 and £400 eyepiece. My plan is to get these.

With F6.3 reducer 945mm focal

5mm = 189x

8mm = 118x

13mm = 72x

21mm = 45x

Thank you

[N3ptune]

Usually when the apparent field of view of the eyepiece is large, so is the price has well has the size of the eyepiece. This will get you a large apparent field of view (AFOV), the "lost in space" effect. Try to look inside an eyepiece with 42 degrees apparent field of view then take a look in another eyepiece with 82 degrees apparent field of view, you will see where the extra money went right away.  

I understand it can be more complicated technically to get high quality views from a large AFOV eyepiece then from a narrow AFOV eyepiece, especially with slower telescope like F5 (and lower numbers). So, in order to get less aberrations in the views and a large AFOV, people will pay for high-end products.

You can read about many aberrations there for instance:

http://umich.edu/~lowbrows/reflections/2007/dscobel.27.html

http://www.handprint.com/ASTRO/ae4.html

If this can help.

[Stu]

The most expensive eyepieces are long focal length, large afov and are specified to work down to, say f4. These are physically larger so contain a lot of glass, and the design, manufacture and QC required to give good edge performance when used in fast scopes is quite challenging.

Good eyepieces are not just about wide fields though, contrast and low light scatter are also important, and these things are affected by the optical polish of the lens elements, the coatings applied and things like blackening of all internal surfaces.

A simple Orthoscopic eyepiece can give results in a 42 degree field which rival those in 100 degree eyepieces. They are comparatively small, simple and cheap though, because they only contain 4 lens elements and are simple to assemble (although good QC is always important). By comparison, an Ethos or ES design has, I believe, 12 elements and is far more complex to manufacture and build.

The benefit is obviously the huge, well corrected field of view. Here are some designs to show the difference, and then a comparison of the fov with a 12.5mm ortho and a 13mm Ethos in your scope!

[icebergahed]

Hi Stu and N3ptune

Thanks for keeping it simple for me. I believe i understand now.

Do i have the correct selection of magnifcations i plan to purchase for a f6.3.? I dont plan to have an army of lenses. I just want to cover most targets in the sky.

Thank you

[Timebandit]

19 minutes ago, icebergahed said:

    I dont plan to have an army of lenses. I just want to cover most targets in the sky.

Thank you

 

 

Unfortunately to cover most targets fully in the sky you do need a fair few eyepieces, due to seeing conditions, magnification required and size of target ect, . That is unless you go down the zoom route.

Personally to get you going i would think something around 5mm , 8mm and 18mm would be a great start and will cover a lot of planetary,lunar and DSO. There are so many types and costs of eyepieces. From super wide fields ,at a cost , to the sharp but small fov and tight eye relief,  of the Ortho.

So to play safe and not to spend a fortune, I think something like the BST starguiders at around £50 each new would be great  eyepieces to get you going . These have very good feedback on this site, Optical wise very good, eye relief i understand of around 16 to 20mm ,and a fov of 60d , a great eyepiece to start with. Therefore a BST 5mm, 8mm and 18mm would certainly be a good choice to get you going at sensible money.

I hope this helps☺

 

 

[Stu]

BSTs sound like a very good option.

The 5mm giving x187 using the reducer should be a nice planetary and lunar eyepiece.

[icebergahed]

Hi

I have brought the 21mm celestron Ultima duo which i am very happy with. Im thinking of keeping to the same range and making them a set. They are around £70-£100 each.

Any comments on these eyepieces would be appretiated.

They have the feature of fitting direct onto my camera t-ring which is an added bonus.

Thank you

[Stu]

The other way to look at this is in terms of the exit pupil each eyepiece gives you. Your suggestions are below:

5mm gives 0.79mm exit pupil

8mm           1.26mm

13mm         2.06mm

21mm         3.3mm

This is actually not a bad range. You can alway suggest more eyepieces, for instance something around the 1mm Exit pupil or x150 would be useful for nights of less good seeing on planets or for globular clusters for instance. Below 1mm there is always a chance that you will see the floaters in your eyes, but I observe down to 0.5mm and sometimes beyond and it is manageable. The 5mm should be fine.

The 13mm will be a nice DSO observing eyepiece as 2mm gives good contrast on low surface brightness objects.

The other one to consider might've something to give you maximum at the low end. A 32mm Plossl would give you a 5mm exit pupil which would work well for filtered views using say a UHC or OIII filter on larger objects.

A potential range, using BST starguiders plus a Plossl would give you:

5mm x189 0.32 deg fov 0.8mm EP

8mm x118 0.51 deg fov 1.3mm EP

12mm x79 0.76 deg fov 1.9mm EP

18mm x52 1.14 deg fov 2.9mm EP

32mm x29 1.69 deg fov 5mm EP

The rings on these charts show the different fields of view with these combinations.

[icebergahed]

Thank you Stu

You've saved me running circles on google trying to find this info.

The Ultima Duos dont come in a 32mm but i will maybe try another brand for that. Whats the program your using to generate the simulation images?

[25585]

I have a TS Optics 32mm 2 inch Erfle. It would be fine for a SCT. They have good eye relief, light transmission & are relatively inexpensive. 65 deg FOV. 

[Louis D]

On 12/25/2017 at 06:34, Stu said:

The 5mm giving x187 using the reducer should be a nice planetary and lunar eyepiece.

Generally it's not recommended to use a high power eyepiece with a focal reducer.  The FR will tend to introduce spherical aberration or other issues only visible at high magnifications.  It's usually best to remove the reducer for high power viewing.  My coma corrector on my Newt can create similar problems at high powers as well.  I sometimes forget to try removing it to see if the view improves.

[Stu]

5 hours ago, Louis D said:

Generally it's not recommended to use a high power eyepiece with a focal reducer.  The FR will tend to introduce spherical aberration or other issues only visible at high magnifications.  It's usually best to remove the reducer for high power viewing.  My coma corrector on my Newt can create similar problems at high powers as well.  I sometimes forget to try removing it to see if the view improves.

Good point Louis, I was not aware of that. The OP said that he would likely want to avoid fitting and removing the reducer so would probably observe with it in all the time. If this causes issues at high power then it is good you pointed it out now as that may change decisions. Thanks!

[Stu]

On 26/12/2017 at 13:28, icebergahed said:

Whats the program your using to generate the simulation images?

It's an app called SkySafari which runs on iOS or Android. It really is excellent and I use it all the time for planning and to help me when observing. It will also control certain mounts via wifi which is very handy.