Help with my first ever barlow lens

[gamermole]

Hello there guys, i have recently gotten into observing the sky after using a pair of binoculars for a while, i bought my first ever telescope, a skywatcher skymax 127 which i have been using and enjoying using the eye pieces provided, i recently bought a 3X barlow lens and when i use this in conjunction with the eyepieces i cant see anything at all, its just a dark blur. the barlow lens can be seen here https://www.rothervalleyoptics.co.uk/rvo-x3-barlow-lens-with-t-thread-125.html

I fear that the 3x lens may be too powerful for this scope? ive also heard that i may need to remove the L shaped eyepiece holder (sorry i dont know the name of this) and use the barlow lens straight into the scope?

Ive yet to have a clear night to try out any method and any advice would be very helpful

[malc-c]

Yes you have basically hit the nail on the head... your scope has a long focal length of 1500mm with a focal ration of f11.81.  Its this long focal length that makes it great for observing the Moon and planets.  With the supplied eyepieces the magnifications are 60x and 150x.   The 3x barlow lens effectively gives a 4500mm focal length so you'll get 180x and 450x with the supplied eyepieces.  At those magnification the depth of field would make focusing difficult, assuming the image could be focused with that combination.  But the main problem would be the focal ratio which would be around f35, meaning that the image will be extremely dark and lack any definition.

The relationship between focal lengths of the telescope, the focal lengths of the eyepieces and the focal ratios are so intertwined that increasing one has a knock on effect.  Increasing magnification by using smaller focal length eyepieces, or adding barlow lenses requires more aperture to gather more light to maintain the same brightness and detail as seen with lower magnifications.

To be honest I would return the 3x barlow and consider getting a decent 6 or 8mm eyepiece.  The image will be slightly higher magnifications, but no so much that the image is too dark.

[Louis D]

Many folks with 127 Maks are trying to get to wider true fields of view rather than higher powers by using Barlows.  I switched to a 2" visual back and put a 2" diagonal on mine to massively increase the true field of view by using widest field of view 2" eyepieces.  Sure, there is some light falloff beyond the field fully illuminated through the 27mm rear port, but the human eye has difficulty noticing it.

[gamermole]

13 hours ago, malc-c said:

Yes you have basically hit the nail on the head... your scope has a long focal length of 1500mm with a focal ration of f11.81.  Its this long focal length that makes it great for observing the Moon and planets.  With the supplied eyepieces the magnifications are 60x and 150x.   The 3x barlow lens effectively gives a 4500mm focal length so you'll get 180x and 450x with the supplied eyepieces.  At those magnification the depth of field would make focusing difficult, assuming the image could be focused with that combination.  But the main problem would be the focal ratio which would be around f35, meaning that the image will be extremely dark and lack any definition.

The relationship between focal lengths of the telescope, the focal lengths of the eyepieces and the focal ratios are so intertwined that increasing one has a knock on effect.  Increasing magnification by using smaller focal length eyepieces, or adding barlow lenses requires more aperture to gather more light to maintain the same brightness and detail as seen with lower magnifications.

To be honest I would return the 3x barlow and consider getting a decent 6 or 8mm eyepiece.  The image will be slightly higher magnifications, but no so much that the image is too dark.

Thank you so much for your reply, do you know whether a 2x barlow lens would work with this telescope? ive found a 6mm eyepiece online if not.

[Cosmic Geoff]

41 minutes ago, gamermole said:

Thank you so much for your reply, do you know whether a 2x barlow lens would work with this telescope? ive found a 6mm eyepiece online if not.

The highest power eyepiece I ever used with my 127mm Mak was 8mm.  Forget the Barlows and buy a decent 8 or 10mm eyepiece. The higher power eyepieces supplied with these kits are notoriously not much good.    When I bought decent eyepieces of 8 and 10mm for my Mak the improvement in performance on double stars was marked and obvious.

[malc-c]

1 hour ago, gamermole said:

Thank you so much for your reply, do you know whether a 2x barlow lens would work with this telescope? ive found a 6mm eyepiece online if not.

One thing that hasn't been mentioned is price.  Decent eyepieces start form around £80.  Decent Barlows,  £100.  Use a £100 barlow with a stock or cheap  eyepiece and you will be wasting your money.  Follow Geoff's advice... invest in a decent branded (Celestron etc) 7mm / 8mm eyepiece.

Conversely, spending £800 on a top flight eyepiece and then using it on a low end scope is also a waste of money - There has to be a balance

[gamermole]

1 hour ago, Cosmic Geoff said:

The highest power eyepiece I ever used with my 127mm Mak was 8mm.  Forget the Barlows and buy a decent 8 or 10mm eyepiece. The higher power eyepieces supplied with these kits are notoriously not much good.    When I bought decent eyepieces of 8 and 10mm for my Mak the improvement in performance on double stars was marked and obvious.

thank you for your excellent advice. i wasnt looking to spend too much on an eyepiece (roughly £50) is there any specific eyepiece you could recomend  for a skywatcher 127.

 

also would this eyepiece be any good in 6mm?

https://www.rothervalleyoptics.co.uk/rvo-68-wa-eyepieces-125.html

[gamermole]

25 minutes ago, malc-c said:

One thing that hasn't been mentioned is price.  Decent eyepieces start form around £80.  Decent Barlows,  £100.  Use a £100 barlow with a stock or cheap  eyepiece and you will be wasting your money.  Follow Geoff's advice... invest in a decent branded (Celestron etc) 7mm / 8mm eyepiece.

Conversely, spending £800 on a top flight eyepiece and then using it on a low end scope is also a waste of money - There has to be a balance

i was only looking to spend around £50 on an eyepiece.

 

can you tell me if this in 6mm would be worth getting over the stock 10mm eyepiece that comes with the scope?

https://www.rothervalleyoptics.co.uk/rvo-68-wa-eyepieces-125.html

[Carbon Brush]

1 hour ago, Cosmic Geoff said:

Forget the Barlows and buy a decent 8 or 10mm eyepiece. The higher power eyepieces supplied with these kits are notoriously not much good. 

Yes definitely. Some of the kit supplied 10mm EPs would be better repurposed as salt pots.

 

I can't speak for the RVO offering.
I have though used some of the BST Starguider EPs.
For the ££ spent they are good.
https://www.firstlightoptics.com/bst-starguider-eyepieces/bst-starguider-60-8mm-ed-eyepiece.html

Is there someone local to you who might lend you an eyepiece?
Don't forget you can get a good idea of views by using the scope on distant objects in the day.

[gamermole]

59 minutes ago, Carbon Brush said:

Yes definitely. Some of the kit supplied 10mm EPs would be better repurposed as salt pots.

 

I can't speak for the RVO offering.
I have though used some of the BST Starguider EPs.
For the ££ spent they are good.
https://www.firstlightoptics.com/bst-starguider-eyepieces/bst-starguider-60-8mm-ed-eyepiece.html

Is there someone local to you who might lend you an eyepiece?
Don't forget you can get a good idea of views by using the scope on distant objects in the day.

Thank you so much, I have just purchased that eyepiece, I will see if it's much of an improvement over the supplied eyepieces. Thank you