Thank you + eyepiece question

[trickybilly]

First I would like to say a big thank you for this community who have helped me to start my hobby some weeks ago and see many beautiful objects so far: Mars, Venus, the Andromeda and Whirlpool galaxy, M42, M35, M36, M38, M41, M45, M57, Hyades and a satellite.

Question: my Skywatcher 200/1200 telescope with 10mm eyepiece gives 120X magnification. What do you recommend to buy next a) a 6mm Goldline eyepiece b) a 2 or 3x Barlow? or something else? I see there are achromatic, apochromatic and "polychromatic" Barlow available... can you please say in short what they mean, and which is the best? Is there any loss of quality using Barlow compared to an eyepiece? My eyepieces are Plössl and I have read on the internet that they have problems with Barlow lenses - is this true?

[SurferSmyth (Ryan)]

good question about the barlows! ill be interested to hear the answers

[JJDOBBER79 (Jas)]

ok, first off, you have had a really good start veiwing all of those objects in a few weeks. Well done. I have a limited understanding myself but I will try and help. I dont know what the different types of barlows mean. I know from what others have told me on this forum that if you buy a QUALITY barlow there should be no difference in the view you get with using a shorter focal length eyepiece. spend about $150 or you will be doing more harm than good. TV barlows are about this much. You mentioned that you have a 10mm plossl, is that the only ep you have? If so, I would be on the lookout for something that is lowest power you can get in 1.25" and a 2x barlow. You can then use this on your 10mm as well. a lot of people on this forum dont use barlows but the fact remains that if you have a limited budget, a barlow can double your arsenal. If you dont have a limited budget, by all means go and buy a Tv/pentax/vixen/ES in every focal length. Hope this helps

[Varangian (John)]

Originally Posted by trickybilly

First I would like to say a big thank you for this community who have helped me to start my hobby some weeks ago and see many beautiful objects so far: Mars, Venus, the Andromeda and Whirlpool galaxy, M42, M35, M36, M38, M41, M45, M57, Hyades and a satellite.

Question: my Skywatcher 200/1200 telescope with 10mm eyepiece gives 120X magnification. What do you recommend to buy next a) a 6mm Goldline eyepiece b) a 2 or 3x Barlow? or something else? I see there are achromatic, apochromatic and "polychromatic" Barlow available... can you please say in short what they mean, and which is the best? Is there any loss of quality using Barlow compared to an eyepiece? My eyepieces are Plössl and I have read on the internet that they have problems with Barlow lenses - is this true?

I honestly don't think you even need a barlow to be honest. A 2X barlow will effectively turn your 10mm into a 5mm eyepiece which is way to much magnification to see anything at all. You'll have a big blurry blob in your eyepiece! I would look at getting something around the 25mm mark if anything (if you haven't already) so you can start to enjoy other night time wonders). Even if you do fork out $150 for a TeleVue barlow (second hand ones can be had on here for $100) you are still limited by the quality of your plossl.
If anything I would be purchasing a 7mm-8mm TMB Planetary (about $50) if you really want higher magnification before I purchased a barlow but as stated above anything under 10mm really gets very little use unless conditions are excellent. I also try to limit the amount of glass between my eye and what I am viewing so I steer well clear of barlows.

[JJDOBBER79 (Jas)]

A 5mm will give 240X. Maybe my eyesight is better than most but I regularly push mine to 300x with only very slight blurriness. IMHO, the advantage of having an object larger in the FOV outweighs the very very slight bluriness that results. The same effect is caused by average seeing most of the time anyway. I used to do the same with my 6" dob as well. Im not saying that you will use it at this mag all the time, but I am happy with the views at 300x at least 50% of the time. Getting out to somewhere dark will certainly produce results at this magnification. Again, just my opinion, a lot of factors do contribute to what is seen at the EP.

[Varangian (John)]

On the average night I am rarely satisfied with my view at 300x but I guess it comes down to personal preference.

I would still go the 6mm-8mm TMB eyepiece. The eye relief is 20mm (so twice the eye relief on your 10mm) and the FOV is about 60 degrees. Keep in mind that a 2X barlow will effectively cut your FOV in half, so a 52 degree plossl will be cut to 26 degrees. The TMB will be a bit better than double the FOV so the object will stay in the eyepiece twice as long.

Also, the TMB is around $50 while a Saxon 2X barlow is around $70 I think. Added to that with the TMB you won't be looking through an extra layer of glass or fumbling around in the dark screwing barlows onto eyepieces.

Just my 2c.

[JJDOBBER79 (Jas)]

good point about the barlow effectively halving your FOV. I have never noticed this before. I have been viewing jupiter recently with my xw10 and 2x TV barlow (300x) and like I said pretty good viewing most of the time. For example observed a quite clear transit and red spot last night. But it does move through the FOV quite quickly. So, this actually is a significant disadvantage to using a barlow that I never considered before. I guess the large FOV is one of the main reasons one spends big bucks on a premium ep. For example, a major deciding factor for most people to purchase say.. an ethos... would be the 100 degrees FOV. Does that mean that if you barlow one of these you will only get 50 degrees. I better go and buy the whole ethos range ASAP....

[barx1963 (Malcolm)]

Originally Posted by Varangian

Keep in mind that a 2X barlow will effectively cut your FOV in half, so a 52 degree plossl will be cut to 26 degrees.

This is not correct (Sorry John). The APPARENT FOV of the ep will still be whatever it was before. So a 52deg plossl will still show the same apparent field however the TRUE FIELD will be halved. So a Televue Plossl in an 8" f6 will yield a TFOV of 1 deg and if you bang it into a 2x barlow it will cut this to 0.5deg.
Just t explain the diff. The TFOV is the area of sky that you can see in the eyepiece, so in this case a 25mm ep barlowed yielding a TFOV would just about be filled by the full moon (which averages around 0.5deg in angular size. The AFOV is the width of the field as it appears to your eye. So if you managed to create an optical system that had zero magnification with a 50deg AFOV and lookat at the full moon, the moon would take of 1% of its width.

It is fairly important to avoid confusion when talking about FOV to be clear as to whether we are talking TFOV or AFOV.

Cheers

Malcolm

[barx1963 (Malcolm)]

To get back to the OPs query. An 8" scope has a "theoretical" maximum power of about 50x per inch which sounds good as it yields 400x, so why not just go and buy a 3mm EP?
Unfortunately for most scopes theoretical and practical power are vastly different and in most cases practical power is more like 10x-20x per inch or around 80x-160x. In good conditions that can be pushed higher. Limiting factors include quality of the optics, focal ratio, seeing conditions, accuracy of collimation, optical quality of the EP, among others.
Increased power does have the advantage that it darkens the background sky, technically it is increasing the power past contrast threshold, but that must be balanced against the other factors mentioned about in particular seeing conditions.
Most deep sky objects will look very nice at less than 130x from experience, so unless you really need higher power I wouldn't bother with a barlow. If a 10mm is your only EP I would look at getting a lower power one first.

Cheers

Malcolm

[AstralTraveller (David)]

I have a 6" f/8 refractor and a 10" f/5 newt, so about the same focal length as you. My wide field eps are 28mm WO UWAN, 20mm, 13mm and 9mm Naglers. The 28mm gets used for the really big splashy objects (eta Carina, M42, NGC 3532 etc) and as a finder ep. Most viewing is with the 20mm and especially the 13mm. The 9mm gets a bit of use but often if I'm using that high a magnification it's on a small object and I switch to the 10mm ortho, which is slightly better on axis than the Nagler. My favourite planetary ep is my 7mm UO HD ortho. Very nice views if you can handle the short eye relief. I also have a 5mm ortho but generally find the seeing doesn't support its use and the eye relief is so short you wind up touching the eye lens with your eye. I've used Teleview barlows but decided against buying one; I just spent a bit longer getting the collection together.

[Varangian (John)]

Originally Posted by barx1963

To get back to the OPs query. An 8" scope has a "theoretical" maximum power of about 50x per inch which sounds good as it yields 400x, so why not just go and buy a 3mm EP?
Unfortunately for most scopes theoretical and practical power are vastly different and in most cases practical power is more like 10x-20x per inch or around 80x-160x. In good conditions that can be pushed higher. Limiting factors include quality of the optics, focal ratio, seeing conditions, accuracy of collimation, optical quality of the EP, among others.
Increased power does have the advantage that it darkens the background sky, technically it is increasing the power past contrast threshold, but that must be balanced against the other factors mentioned about in particular seeing conditions.
Most deep sky objects will look very nice at less than 130x from experience, so unless you really need higher power I wouldn't bother with a barlow. If a 10mm is your only EP I would look at getting a lower power one first.

Cheers

Malcolm

Malcolm, of course you are 100% correct thank you for clarifying. I don't step away from my opinion of a 6-8mm TMB over the barlow. Cheers, John.

[barx1963 (Malcolm)]

Originally Posted by Varangian

Malcolm, of course you are 100% correct thank you for clarifying. I don't step away from my opinion of a 6-8mm TMB over the barlow. Cheers, John.

No worries John. I have never looked through a TMB EP so obviously cannot comment on them. I was however stating some general principles in relation to power and magnification in telescopes that many beginners may not be aware of.

Malcolm

[Varangian (John)]

Originally Posted by barx1963

No worries John. I have never looked through a TMB EP so obviously cannot comment on them. I was however stating some general principles in relation to power and magnification in telescopes that many beginners may not be aware of.

Malcolm

I meant to reply to your earlier post re. AFOV and TFOV.

It's not a world beater but the TMB is superior to any plossl I've looked through and that also applies to the fake TMBs as well.

It's great that some experienced posters get into the beginners threads to help out. It's really appreciated. Sometimes beginners help beginners because these threads are ignored.

Cheers.

[Camelopardalis (Dunk)]

Originally Posted by JJDOBBER79

I guess the large FOV is one of the main reasons one spends big bucks on a premium ep. For example, a major deciding factor for most people to purchase say.. an ethos... would be the 100 degrees FOV. Does that mean that if you barlow one of these you will only get 50 degrees. I better go and buy the whole ethos range ASAP....

FWIW, the AFOV is one of the reasons people buy an Ethos, one of the others is the optical quality, which was the best TV had made

If you have an addictive personality I suggest you NEVER look through one because it's a slippery slope