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Old Sunday 9th July 2017, 22:05   #26
DRodrigues
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Indeed, but it means 100x for just the price of the adapter as the Radian is from his girlfriend's astro gear...
Yes, I noticed. My comment resulted from comparing 96x >70 AFOV with 100x 60 AFOV - probably will not be very appealing...
However, the Radian will show better contrast and definition. Now a Baader Morpheus 4.5 will result on 113x with 76, that will please more most... Eventually the Radian will be a good test to Henning decide if he should invest in an astro ep with higher mag and AFOV...
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Old Sunday 9th July 2017, 22:30   #27
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Hi,

yes indeed 96x at the top end of the extended zoom would be nicer... but he doesn't have the extender yet... so 100x for almost free is a good thing...

Joachim
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Old Monday 10th July 2017, 10:49   #28
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Hi Joachim,

Quote:
Originally Posted by jring View Post
Indeed, but it means 100x for just the price of the adapter as the Radian is from his girlfriend's astro gear...

It might be interesting to know what other EPs are available - maybe a 1.25" barlow would give some more good options...
We had a look at the astro stuff now, and here's what we found in 1.25":

- Televue Radian 5 mm
- Televue Nagler 13 mm
- Televue 3x Barlow

So (provided the 3x Barlow fits physically) the available magnifications would seem to be 38, 100, 115, 300.

A relatively unexpensive upgrade might be a 2x Barlow, would would yield 200 with the 5 mm Radian. I'm not sure though if that's a sensible magnification with the Kowa - my girlfriend stresses there's a rule of thumb not to use magnifications beyond 2 x front lens diameter / mm, so the highest sensible magnification would be 176 for the Kowa.

With the Kowa 1.6 Extender, we'd be at 160 with the 5 mm Radian, which would be a somewhat more expensive upgrade.

How important is apparent field of view for planetary observation? Some sites seem to stress magnification over field of view for that application ...

Regards,

Henning
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Old Monday 10th July 2017, 12:59   #29
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Hi,

nice stuff... definitely try the 13mm Nagler for a super wide 39x view - that's 2.1 deg or 36/100m - that's almost as much as the zoom has at 25x (2.4 deg or 42/1000m).

The school of thought that field of view is not needed for planetary viewing usually expects your instrument to be mounted on an equatorial mount with automatic tracking... as long as this is not the case and you need to keep the planet in your fov manually, you will love every degree of your fov...

That rule of thumb is indeed a good one, but you need to know when you can deviate from it. It assumes average eyesight of the observer. Depending on the state of your eyesight, higher magnification can be beneficial or not.

Joachim
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Old Monday 10th July 2017, 16:17   #30
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The main factor is the Seeing or steadiness of the air and the transparency, clarity. The first is important for planets.
I don't know how the Kowa 88mm cools, but astro refractors need about 20minutes. Newtonians 30 mins and Maksutovs up to an hour. Say 20C to 5C outside.
If the temperature inside and outside is the same you are lucky.
In autumn this can happen.
Observe over grass not concrete or asphalt. Or over water.

If your eyes are young and clear then you can probably easily use 0.3mm exit pupils. If not maybe larger.

The Kowa is I think a good scope and 200x should be readily available and usable.

The higher power for good scopes in good conditions for objects above 40 deg elevation is 65 to 70x per inch. However, 50x per inch is usually sufficient. Mars in particular takes high powers, also Jupiter's moons and double stars.

I think a long focus 100mm refractor might better the Kowa but maybe not by much.

My 100mm f/12 Pentax, the makers demonstrator, was fully usable at 300x, although 200x and 250x was used more often. Testing showed no problems at 400x, but this was not for observing, just to see how good the optics were.

A Televue Barlow and the Nagler should be fun.

There are micro hand drives for scopes but maybe not suitable for high powers.

I used a Slik 88 tripod and a 3x teleconverter and Japanese monocular converter on a Vivitar Series 1 600mm f/8 solid Cat and cleanly separated both pairs of epsilon Lyrae at 180x. Around 2.5 arcseconds separations. Not bad for a photo lens used by policemen.

P.S.
I used a monocentric eyepiece, possibly made by H.Dall and a Tolles on planets. These have tiny fields of view. It is easier with a long straight through scope.

P.P.S
Although a Barlow might be marked as 2x it might be 1.8x or 2.2x as the actual position of the Barlow and eyepiece and light train is critical and it will vary with different eyepieces.
Usually, though, Televue markings are accurate for their own eyepieces, but it would be interesting to know the true magnification with any particular setup.
It is a little silly to quote a magnification of 178x or 154x when the eyepiece focal length varies by 5% or more from that marked and the Barlow position is critical. It is more sensible to round to
180x and 155x.

Even skilled astronomers do this, but assigning such accuracy to magnifications is slightly wishful thinking.

Last edited by Binastro : Monday 10th July 2017 at 16:47.
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Old Monday 10th July 2017, 19:09   #31
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The best time to view planets are when they are highest in the sky.
In the south from here, at least the Superior planets.

This means that the only movement needed with a fixed tripod is horizontal.
This will keep the planet more or less central.
I think there are several manual fine drives available for tripods.

High magnification is useful to find faint satellites of Saturn, for instance.
This darkens the sky revealing fainter 'stars'.
It also increases the apparent distance from Saturn's rings to the faint moon, sometimes allowing the rings to be excluded from the field. Here a flat field is useful.
With Jupiter the planet can also be excluded at high power to better see its moons.

One can also use an occulting eyepiece.

The magnification of 96x rather than 95x was given for the Acuter as this gives a clue to the focal length of 480mm nominal.
With main mirror focus scopes the focal length changes, drastically with smaller scopes, as one focuses.
So all magnifications given are questionable, particularly if a star diagonal or prism is used.

Uncertainty of magnification also applies to Barlows.

Last edited by Binastro : Monday 10th July 2017 at 21:41.
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Old Monday 10th July 2017, 23:20   #32
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Hi Joachim,

Quote:
Originally Posted by jring View Post
The school of thought that field of view is not needed for planetary viewing usually expects your instrument to be mounted on an equatorial mount with automatic tracking... as long as this is not the case and you need to keep the planet in your fov manually, you will love every degree of your fov...Joachim
Ah, makes perfect sense - thanks! :-)

Quote:
Originally Posted by jring View Post
That rule of thumb is indeed a good one, but you need to know when you can deviate from it. It assumes average eyesight of the observer. Depending on the state of your eyesight, higher magnification can be beneficial or not.
Fully corrected, I'm at 120%, so maybe 200x will work out!

Regards,

Henning
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Old Monday 10th July 2017, 23:35   #33
Hauksen
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Hi Binastro,

Quote:
Originally Posted by Binastro View Post
The higher power for good scopes in good conditions for objects above 40 deg elevation is 65 to 70x per inch. However, 50x per inch is usually sufficient.
Ah, 50/in = 2/mm ... that's the same rule of thumb then :-)

Quote:
Originally Posted by Binastro View Post
P.P.S
Although a Barlow might be marked as 2x it might be 1.8x or 2.2x as the actual position of the Barlow and eyepiece and light train is critical and it will vary with different eyepieces.
Usually, though, Televue markings are accurate for their own eyepieces, but it would be interesting to know the true magnification with any particular setup.
It is a little silly to quote a magnification of 178x or 154x when the eyepiece focal length varies by 5% or more from that marked and the Barlow position is critical. It is more sensible to round to
180x and 155x.
Thanks! :-) I had already some suspicions in that regard ... I noticed that the focal length of the Kowa 883 was sometimes listed as 510 mm, and I think the table of Explore Scientific eyepieces showed most of them with a slightly different focal length than their nominal value too!

Is there a way to determine in advance which Barlow will fit the Kowa with which adapter? The "knurled knob" version is advertised as easier to operate since you don't need a wrench, but the "grub screw" version is flatter and thus more likely to accept the Televue 3x Barlow (or a 2x Barlow we might buy), but I haven't found any explanation on how to measure this beforehand.

Regards,

Henning
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Old Monday 10th July 2017, 23:45   #34
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Hi Binastro,

Quote:
Originally Posted by Binastro View Post
With Jupiter the planet can also be excluded at high power to better see its moons.
Thanks, we'll try this! Jupiter is favourite of my girlfriend, both for the moons and for the Great Red Spot! :-)

Regards,

Henning
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Old Tuesday 11th July 2017, 00:03   #35
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With the Kowa 88mm I would expect when younger to see 5 of Saturn's moons.
Titan, Rhea, Iapetus at one elongation (It has a dark and light side so varies in brightness), Dione and Rhea.

My friend saw these with a Royal 60mm scope. We were young then.

However, now Saturn is south of the celestial equator, so is much better seen in the southern hemisphere.

High power also darkens Saturn's ring surface brightness giving less glare in addition to providing more apparent distance to a faint moon.

I have seen Enceladus, (possibly with life forms there), with a 150mm Maksutov from a town centre balcony.
Not sure if the Kowa 88m could show it.

I don't know about Barlows for the Kowa, as I have never seen a Kowa 88mm. It is too expensive to buy for no reason.

I think the Kowa 88 is better than my 127mm Maksutov, which is not great, but maybe not as good as the 150mm Maksutov, 100mm Pentax or 120mm D. Hinds objective refractor, or indeed a very old Ross triplet 100mm f/12 refractor that a noted astronomer uses. It was George Alcock's scope.
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Old Tuesday 11th July 2017, 07:21   #36
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Is there a way to determine in advance which Barlow will fit the Kowa with which adapter? The "knurled knob" version is advertised as easier to operate since you don't need a wrench, but the "grub screw" version is flatter and thus more likely to accept the Televue 3x Barlow (or a 2x Barlow we might buy), but I haven't found any explanation on how to measure this beforehand.
Hi,

yes, the Kowa 88mm has a focal length of 510mm.

You could measure the change of focal point of the barlow on an astro scope by measuring the focal point without and with barlow and the same EP and subtracting for a value in mm. But this won't help a lot as you don't know the actual travel distance inside the Kowa and can't measure focal points there either.
My Baader 2.3x screw on barlow (from the Baader zoom kit) puts the focal point quite a bit to the outside - maybe 30mm...
I'm quite sure that a spotter will not have that much focus travel, but since it's to the outside, you could use a 1.25" extension or just not fully insert barlow and/or EP.

So please don't buy a barlow without first having tried the existing 3x.

Joachim
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Old Tuesday 11th July 2017, 09:35   #37
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Hi Binastro,

Quote:
Originally Posted by Binastro View Post
I think the Kowa 88 is better than my 127mm Maksutov, which is not great, but maybe not as good as the 150mm Maksutov, 100mm Pentax or 120mm D. Hinds objective refractor, or indeed a very old Ross triplet 100mm f/12 refractor that a noted astronomer uses. It was George Alcock's scope.
If my Kowa is the ball park at least, that's actually pretty exciting :-)

It must be great to be around a telescope with historic significance like Alcock's! On a recent visit to the historic observatory at Bergedorf, I really enjoyed the historic atmosphere too - the observatory was built 100 years ago, and the original set of telescopes is still pretty much in place, and is still used for astronomical work.

Regards,

Henning
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Old Tuesday 11th July 2017, 09:40   #38
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Hi Joachim,

Quote:
Originally Posted by jring View Post
But this won't help a lot as you don't know the actual travel distance inside the Kowa and can't measure focal points there either.
Ah, in that case, I'll just have to try with the Barlow we already have. I've just ordered the "flat" astro adapter and am looking forward to trying it out as soon as it arrives (and as soon as we enjoy clear sky, for a change :-)

Many thanks to everyone for all the great tips!

Regards,

Henning
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Old Wednesday 2nd August 2017, 20:12   #39
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Hi,

Where you get this 510mm focal lenght?
Isn't it 343mm, did i miss something?
I have Kowa 883 / 25-60 zoom and wondering too, that did i buy extender or a few astro ep

Regards,

Lazy_ferret

Last edited by lazy_ferret : Wednesday 2nd August 2017 at 20:14.
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Old Wednesday 2nd August 2017, 21:27   #40
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Hi,

343mm is the length of the body. The focal length is certainly longer as there is the eyepiece and also some extra light path in the image erecting prism...

Also Kowa fixed mag EPs are usually labelled with their focal length - and 17mmx30=510mm...

Joachim
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Old Wednesday 2nd August 2017, 22:07   #41
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Hi,

343mm is the length of the body. The focal length is certainly longer as there is the eyepiece and also some extra light path in the image erecting prism...

Also Kowa fixed mag EPs are usually labelled with their focal length - and 17mmx30=510mm...

Joachim
That's interesting as Kowa on Facebook told me the focal length is 500mm, so something's slightly amiss somewhere.
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Old Thursday 3rd August 2017, 09:04   #42
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That's interesting as Kowa on Facebook told me the focal length is 500mm, so something's slightly amiss somewhere.
Hi,

well the difference between 500 and 510mm is not so big... in astro scopes that might be within tolerance - with spotters with their small focus travel, things need to be a bit more precise...

Joachim
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Old Thursday 3rd August 2017, 16:41   #43
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Hi jring,
Ok, thanks for clarification.

Lazy_ferret
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Old Saturday 12th August 2017, 09:05   #44
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Hi,

I tested kowa 883 last night and look at the moon with many (ES and BAADER) oculars and kowa adapter.
I notice that "infocus" is not enough. So i must buy extender for stargazing.

Daytime with birdwatcing there is no broblem for ep what i have, infocus is enough but barely. There is allmost nothing left when you turn the focuser knob. Maybe some eyepiece it might be a broblem.

Kowa zoom lens is good and there is no CA, IF you look at exactly middle of ep.
Otherways there is very little blue in the view when you look at moon.
Daytime i dont notice any CA at all.
All and all kowa's zoom is good ep.

lazy_ferret

Last edited by lazy_ferret : Saturday 12th August 2017 at 09:24.
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Old Saturday 12th August 2017, 13:02   #45
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Hi,

I tested kowa 883 last night and look at the moon with many (ES and BAADER) oculars and kowa adapter.
I notice that "infocus" is not enough. So i must buy extender for stargazing.

...

lazy_ferret
With what adapter model?
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Old Saturday 12th August 2017, 13:14   #46
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With what adapter model?
It is kowa's own model.
Tsn-as1.25g/tsn-as1.25k astro adapter

lazy_ferret

Last edited by lazy_ferret : Saturday 12th August 2017 at 13:26.
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Old Saturday 12th August 2017, 13:20   #47
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Yes, but there are 2 Kowa models...
Yours have external screws?
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Old Saturday 12th August 2017, 14:03   #48
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Yes, but there are 2 Kowa models...
Yours have external screws?
Yes there is external screws
Look like this:
http://www.teleskop-express.de/shop/...ng-scopes.html

Edit: strange, it not open if i push the link? But works if i open it a new tab.

Last edited by lazy_ferret : Saturday 12th August 2017 at 14:09.
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Old Saturday 12th August 2017, 16:05   #49
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Yes there is external screws
Look like this:
http://www.teleskop-express.de/shop/...ng-scopes.html

Edit: strange, it not open if i push the link? But works if i open it a new tab.
Hi,

there is another adapter with grub screws - less easy to use but a little more backfocus...

http://www.teleskop-express.de/shop/...ng-scopes.html

Joachim
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Old Saturday 12th August 2017, 17:55   #50
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Hmm... So there is two option for adapter.
I'm little confuced here.
Pleace explain that what purpose for is this two options?

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