47 replies to this topic

[Kasmos]

 

Both are excellent, really surprisingly good - however the Towa is actually quite a bit better. Sharper, more contrast - seemingly less scatter. There is quite a bit of scatter with the Pentax.

The views of flowers/birds etc through the Towa are stunning.

Perhaps the Pentax might be better at night.

I'm surprised since these Pentaxes have always been praised for their performance and not so much for the Towas. I have the Tasco version of the  of it (It was a freebie since the owner wasn't impressed with it) I've never really tested it, but between your comments and a recent one by desitter I should try it and see if I can get it to perform well.

[Kasmos]

I forgot to say that the scattering in the Pentax might be that it's not baffled or blackened well? I've noticed this when building and testing some scopes made from parts and on an Edmund finder that has a shiney interior.

[Princess Leah]

I'm surprised since these Pentaxes have always been praised for their performance and not so much for the Towas. I have the Tasco version of the  of it (It was a freebie since the owner wasn't impressed with it) I've never really tested it, but between your comments and a recent one by desitter I should try it and see if I can get it to perform well.

Hi Kasmos,

I have tried the Tasco version, wasn't good. Was that a Kenko? I can't remember....or was it circle Z?

With Towa I have found similarities with Synta - it's a bit pot-luck. One or two have been poor/useless.

I have a Synta Celestron Firstscope 90's 80mm F11, it's actually better than my equivalent Vixen.

The Pentax is excellent, but you could be forgiven for thinking the Towa was a small Takahashi. For close nature observation it's better than my 80CF Triplet.

I worked hard on the Pentax as it's so good, it also has a good focuser.

Just isn't that good.

[Princess Leah]

I forgot to say that the scattering in the Pentax might be that it's not baffled or blackened well? I've noticed this when building and testing some scopes made from parts and on an Edmund finder that has a shiney interior.

I thought that too. Especially since I had flocked the Towa completely. 

The thing is, the Pentax lens can be unscrewed and screwed into the Towa to compare.

I only realised this after exhausted myself with comparison, I only had one set of 50mm rings - so I had to repeatedly loosen one OTA and replace with the other...!

[Kasmos]

Hi Kasmos,

I have tried the Tasco version, wasn't good. Was that a Kenko? I can't remember....or was it circle Z?

With Towa I have found similarities with Synta - it's a bit pot-luck. One or two have been poor/useless.

I have a Synta Celestron Firstscope 90's 80mm F11, it's actually better than my equivalent Vixen.

The Pentax is excellent, but you could be forgiven for thinking the Towa was a small Takahashi. For close nature observation it's better than my 80CF Triplet.

I worked hard on the Pentax as it's so good, it also has a good focuser.

Just isn't that good.

My Tasco is a Circle T Towa and from the early 60s so you'd think it would be pretty good, but I haven't really used it so I'm just going by what the former owner said. Everybody praises the Vixen C80, but in 2 side by side tests I thought my Mizar 68/1000 gave sharper images. I have 2 C80s now and the second one appeared to work very well one evening when viewing Saturn, so those two need to go up against each other and be evaluated again. 

[Princess Leah]

That's pretty old! How old do you think my Greenkat is?

 

I should have said the Towa/Greenkat is in perfect condition, where as the Pentax objective seems to have degraded coatings in places. Perhaps that could cause more scatter?

[deSitter]

My Tasco is a Circle T Towa and from the early 60s so you'd think it would be pretty good, but I haven't really used it so I'm just going by what the former owner said. Everybody praises the Vixen C80, but in 2 side by side tests I thought my Mizar 68/1000 gave sharper images. I have 2 C80s now and the second one appeared to work very well one evening when viewing Saturn, so those two need to go up against each other and be evaluated again. 

My 50/600mm is outstanding but only got that way by re-seating the lenses repeatedly and tightening the ring pretty firmly.

 

-drl

[Princess Leah]

It is strange how fickle they can be.

[deSitter]

It is strange how fickle they can be.

They tend to have sloppy mechanics relative to more premium brands. Optics are very much all over the place. Terra had a terrible 60mm - "I can still hear that one barking" she said after getting rid of it.

 

Fortunately there are very few mechanical problems that cannot be mitigated or eliminated.

 

-drl

[Princess Leah]

I had a Towa lens that seemed to haunt me for over a year. Always threatened to perform marvelously, I wasted too much time on it.

Fate played a hand, when I dropped it by accident, and it shattered.

Only lens I have ever broken.

At first I was annoyed and then I felt a great sense of relief.....

[Princess Leah]

They tend to have sloppy mechanics relative to more premium brands. Optics are very much all over the place. Terra had a terrible 60mm - "I can still hear that one barking" she said after getting rid of it.

 

Fortunately there are very few mechanical problems that cannot be mitigated or eliminated.

 

-drl

I have found the focuser to be quite rough on the 50/600 despite improving it with Teflon.

How did you find yours?

I may need to replace the rack as it is quite worn in places.

 

I did try switching the Pentax focuser for the Towa.

However I was surprised to see that despite the bigger aperture of the flocked Pentax drawtube, it actually degraded the image somewhat my reducing contrast.

The narrow aperture of the Towa focuser seems to act as another baffle.

Sometimes it doesn't pay to 'open up' these scopes too much.

[Kasmos]

That's pretty old! How old do you think my Greenkat is?

 

I should have said the Towa/Greenkat is in perfect condition, where as the Pentax objective seems to have degraded coatings in places. Perhaps that could cause more scatter?

The knobs are the same as on my Penncrest so going by them, I'd estimate about 1969-70

[Princess Leah]

The knobs are the same as on my Penncrest so going by them, I'd estimate about 1969-70

Jings! That's older than me. 

Thanks.

[Princess Leah]

Could degraded coatings with the Pentax cause more scatter/soften the image?

Im guessing the Pentax is 1950s?

[deSitter]

I have found the focuser to be quite rough on the 50/600 despite improving it with Teflon.

How did you find yours?

I may need to replace the rack as it is quite worn in places.

 

I did try switching the Pentax focuser for the Towa.

However I was surprised to see that despite the bigger aperture of the flocked Pentax drawtube, it actually degraded the image somewhat my reducing contrast.

The narrow aperture of the Towa focuser seems to act as another baffle.

Sometimes it doesn't pay to 'open up' these scopes too much.

The focuser is very nice by any standard. It has a drawtube.

 

-drl

[deSitter]

Could degraded coatings with the Pentax cause more scatter/soften the image?

Im guessing the Pentax is 1950s?

No, unless the coating itself had become translucent somehow.

 

-drl

[Princess Leah]

There is some slight translucent marring.

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[deSitter]

There is some slight translucent marring.

That sort of haze is likely a glass problem, not a coating problem. And I don't think there is much to be done about it. That is a bad problem sad to say. Did you get this from Japan?

 

-drl

[k5apl]

FYI 

My experience with hazy or transluscent objectives might be of some help.  I have found that full strength Acetone used to clean the

objective glass can leave this haze (I am using Acetone from the box stores).  And I have found that some cleaners and home made solutions leave a haze.  I have been using, with good results, a mixture of distilled water, drop of DAWN soap, and a small amount of

Acetone (exact ratios are available on the web).  A final rinse of the clean glass with distilled water, and its good to go.

I do Not want to hijack these posts; only offer an alternative way to possibly fix the objective.

Wes

[Princess Leah]

FYI 

My experience with hazy or transluscent objectives might be of some help.  I have found that full strength Acetone used to clean the

objective glass can leave this haze (I am using Acetone from the box stores).  And I have found that some cleaners and home made solutions leave a haze.  I have been using, with good results, a mixture of distilled water, drop of DAWN soap, and a small amount of

Acetone (exact ratios are available on the web).  A final rinse of the clean glass with distilled water, and its good to go.

I do Not want to hijack these posts; only offer an alternative way to possibly fix the objective.

Wes

Great tip, thanks.

Not sure if it effects the optics , it's only visible at a certain angle, extreme off-axis so to speak.

I got it in local charity shop.

[Princess Leah]

The performance from this little Towa is quite unbelievable - as a spotting scope at least.

It's really hard to believe its 50mm aperture. It's useful terrestrially as the small aperture cuts through turbulence. It reframes my thinking as to how much aperture you need when birdwatching.

I'm watching the buzzards on the hill in the attached photo through an upstairs window and the detail at 30X -40X is quite amazing.

 

Im experimenting with a Baader micro focuser - it's a great addition. I prefer the Celestron prism to the Baader T2 prism- transmission is slightly higher.

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[Princess Leah]

I believe I discovered (and fixed) the source of the glare in the Pentax.

 

Viewing the moon with the Pentax for the first time, I saw bright halos around the moon.

I went indoors and pointed the scope to a bedroom light and the reflection was actually coming from inside the lens cell, where the matt black paint previously was.

Anyway I flocked the entire thing and it now gives some excellent views of the moon. 

I would actually say now, that scatter is very minimal in this scope, and because of the relative wide draw-tube, the entire FOV is well illuminated even with a 20mm 68.

 

However the view through the Towa is a different class altogether. In fact at around 60X it is the best view of the moon I have ever seen.

A caveat to that is, although my Uncle sometimes loans me his Vixen FL 102S, I have never looked through a Takahashi.

Very curious now.

[Princess Leah]

What an ordeal

 

I would just cut an inch off the end of the tube, drill some new holes for the focuser and sight and there you go! I have done this - it was very straightforward work. Cutting the tube square is done using blue painter's tape to make a precisely square channel to guide the hacksaw.

 

-drl

Indeed. But you still have to work out a way on how to connect the 1.25 inch diagonal nosepiece to the tube.  Cutting down the tube wouldn't solve that. Plus I have plenty of those cheap nosepieces lying around.