Questions Regarding Telecompressors (Lens Turbo II)

butangmucat · 11-17-2016, 07:17 PM

Hello,

I have just received my Lens Turbo II in K mount and have tested my FA43 and Volna 50/1.8 lens with it and my Sony a5000. However I am a bit confused with some of the math regarding aperture in terms of light intensity, and the DOF.

As I have read, the Lens Turbo II is a telecompressor with a 0.73x crop factor, and the 135 equivalent focal length of my Volna 50/1.8 with Lens Turbo II should be 50mm*1.5*0.73 ~= 55mm. This is what I am sure about the Lens Turbo II.

Some reviews say that for the equivalent aperture in terms of light intensity, it works like f1.8*0.73 ~= f1.3, however when I research on the Nikon E-series, which also used a telecompressor, I got:

Quote:

The E series uses a unique additional optical system that enables the small sensor to capture the field of view of a 35mm film, with a crop factor of 1. This comes not at the expense of the lightness of the lenses, because the light is bundled to the 2⁄3 inch CCD sensor with approximately 1⁄16 smaller area. The result is approximately 4 stops (2^4 = 16) more light at the small sensor compared to a full-frame sensor. Therefore the camera has a minimum full-frame sensitivity of ISO 800 which is equivalent to ISO 50 at 2⁄3 inch.

Now I am not quite sure how to work out the equivalent aperture in terms of light intensity.

Finally, I found next to none useful information on how to work out the DOF when using the Lens Turbo II. Some say the hyperfocal scale will line up others say it will not. And also no information on how lens correction profiles will behave.

Any information will be welcome.

Sincerely

**UncleVanya** · 11-17-2016, 09:27 PM - **1 Like**

I haven't used one but I have been studying them for a long time. In theory the f1.3 is correct. The Nikon you mentioned involved a much larger reduction and was expressed as ISO rather than aperture since the numbers were rather more confusing.

The dof should be close to "normal" because your subject to camera distance and fov should be that of the full frame projection of the lens. The 5mm difference in effective focal length may slightly skew things.

surfar · 11-17-2016, 10:27 PM

1.1 fl....one stop reduction in aperture...except with the speed booster SUPER model...it reduces a bit more and 1and a third stops...point65 reduction from memory.

11-17-2016, 07:17 PM	#1
butangmucat Veteran Member Join Date: Jul 2016 Posts: 709	Questions Regarding Telecompressors (Lens Turbo II) Hello, I have just received my Lens Turbo II in K mount and have tested my FA43 and Volna 50/1.8 lens with it and my Sony a5000. However I am a bit confused with some of the math regarding aperture in terms of light intensity, and the DOF. As I have read, the Lens Turbo II is a telecompressor with a 0.73x crop factor, and the 135 equivalent focal length of my Volna 50/1.8 with Lens Turbo II should be 50mm1.50.73 ~= 55mm. This is what I am sure about the Lens Turbo II. Some reviews say that for the equivalent aperture in terms of light intensity, it works like f1.8*0.73 ~= f1.3, however when I research on the Nikon E-series, which also used a telecompressor, I got: Quote: The E series uses a unique additional optical system that enables the small sensor to capture the field of view of a 35mm film, with a crop factor of 1. This comes not at the expense of the lightness of the lenses, because the light is bundled to the 2⁄3 inch CCD sensor with approximately 1⁄16 smaller area. The result is approximately 4 stops (2^4 = 16) more light at the small sensor compared to a full-frame sensor. Therefore the camera has a minimum full-frame sensitivity of ISO 800 which is equivalent to ISO 50 at 2⁄3 inch. Now I am not quite sure how to work out the equivalent aperture in terms of light intensity. Finally, I found next to none useful information on how to work out the DOF when using the Lens Turbo II. Some say the hyperfocal scale will line up others say it will not. And also no information on how lens correction profiles will behave. Any information will be welcome. Sincerely

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Lens Turbo II PK-NEX First Impression	chaosteo	Canon, Nikon, Sony, and Other Camera Brands	41	04-17-2020 06:37 AM
Focal reducers - Lens Turbo II or Camdiox?	kerttamm	Canon, Nikon, Sony, and Other Camera Brands	9	04-25-2017 03:28 PM
Lens Turbo II with Sony QX1?	butangmucat	Canon, Nikon, Sony, and Other Camera Brands	6	11-07-2016 01:07 PM
3 Questions regarding specialised settings in K1	Mattox	Pentax Full Frame	4	10-16-2016 09:38 AM
New Lens Turbo II generation now available for Pentax lense	LFLee	Canon, Nikon, Sony, and Other Camera Brands	8	06-03-2014 01:33 AM

11-17-2016, 09:27 PM - 1 Like	#2
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,459	I haven't used one but I have been studying them for a long time. In theory the f1.3 is correct. The Nikon you mentioned involved a much larger reduction and was expressed as ISO rather than aperture since the numbers were rather more confusing. The dof should be close to "normal" because your subject to camera distance and fov should be that of the full frame projection of the lens. The 5mm difference in effective focal length may slightly skew things.

11-17-2016, 10:27 PM	#3
surfar Pentaxian Join Date: Jan 2015 Location: mid nth coast,nsw Photos: Gallery Posts: 6,144	1.1 fl....one stop reduction in aperture...except with the speed booster SUPER model...it reduces a bit more and 1and a third stops...point65 reduction from memory.